TK 
308 
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1894 


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>^x  J- 

THE  UNIVERSITY 

OF  CALIFORNIA 

LOS  ANGELES 


•'-• 


41 


HARTMANN  &  BRAUN 

Bockenheim-Frankfort  o.  M. 


Electrical  Measuring  Instruments. 


Electrical  Exhibition 
PARIS  1881. 


Electrical   Exhibition 
TURIN 


Inventions  Exhibiti 
LONDON  1885. 


CATALOGUE 


of 


Electrical  Measuring  and  Je$ 


Electrical  Engineers 


at 


TEPLITZ  1879. 


BOCKENHEIM-FRANKFORT  °M. 


1894. 


ST.  PETERSBURG 

1886 
Diploma. 


CHICAGO 

1893 
8  Awards. 


-  e\? 
1 1-1 1 1 1 1 1 1 1 


inted  at  August  Ostcrrieth's  Works,  Frankfort  o/M. 


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Mssrs.  Hartmann  &  Braun's  »  «>, 

Exhibit  at  the  Worlds  Fair,  Chicago  1893,*)      "** 

Mssrs.  Hartmann  &  Braun  have  a  splendid  exhibit  at  Chicago.  On  a  floor 
space  of  100  m2  in  the  vast  Electricity  Hall  they  have  erected  a  magnificent 
pavilion  wherein  to  house  their  exhibits.  The  design  of  the  pavilion  is  Italian 
Renaissance  enriched  with  ornamental  plaster  work.  In  the  centre  of  the  facade 
stands  the  statue  of  a  female  typifying  Science  as  applied  to  Electricity,  and 
tendering  in  her  hand  a  laurel  wreathed  medallion  of  William  Weber,  the  ori- 
ginator of  our  electro-magnetic  standards.  The  interior  of  the  pavilion  is  de- 
corated with  a  similar  magnificence.  The  columns  of  the  four  large  entrances, 
which  are  hung  with  splendid  draperies,  and  the  pillars  carrying  the  roof,  form 
a  series  of  bays  round  the  pavilion  walls  on  which  the  various  classes  of  test 
instruments  are  mounted  against  a  pale  green  merino  "background.  The 
contrast  between  the  elaborate  and  handsome  polished  wood  work  and  the 
rich  draperies,  with  the  highly  finished  surfaces  of  the  various  instruments, 
renders  the  entire  exhibit  exceptionally  magnificent.  Each  bay  is  surmounted 
either  with  a  medallion  of  Ohm,  Ampere,  Volt  a,  Watt,  Coulomb, 
Faraday,  in  carton-pierre  or  with  a  shield  bearing  the  names  of  Gauss, 
Henry,  Franklin,  Morse,  Reis,  Kohlrausch.  The  bust  of  the  cele- 
brated German  Scientist  W.  yon  Siemens,  a  work  by  Hildebrand,  is  placed 
under  a  canopy  whose  draperies  form  a  dark  room  for  Photometry  if  required. 
Messrs.  Hartmann  &  Braun's  pavilion  is,  in  fact,  a  Memorial  Hall  for  the 
scientists  whose  researches  are  embodied  in  the  instruments  exhibited,  as  well 
as  a  site  for  the  display  of  the  firm's  manufactures. 

The  pavilion  includes,  in  addition  to  a  complete  collection  of  their  various 
instruments,  an  electrical  laboratory  completely  equipped  for  all  classes  of  mea- 
surements (Figs.  2  and  3).  The  collection,  of  which,  in  most  instances  dupli- 
cates are  shown  connected  and  ready  for  use,  is  partly  housed  in  beautiful 
plate  glass  cabinets  and  partly  in  table  cases,  and  comprises:  Mirror  Galvano- 
meters and  suitable  Telescopes  for  use  therewith;  a  complete  set  of  the  Kohl- 
rausch Instruments;  Standards  made  in  accordance  with  those  of  the  Imperial 
Physico -Technical  Laboratory;  Accurate  Rheostats;  Bridges  and  Resistance- 
measuring  apparatus  for  technical  purposes;  accurate  instruments  for  measuring 
Current  and  determining  Potential  and  various  apparatus  for  Lecture  Room  and 
Demonstration  purposes. 

Various  classes  of  Volt-  and  Amperemeters  for  use  on  direct  or  alternating 
currents;  Ohm-  and  Wattmeters;  Accoustic  Voltmeters  and  Supply  meters;  Milli- 
amperemeters  for  medical  purposes;  electrical  Pyrometers  and  Telethermometers 
are  also  shown  in  14  different  groups  on  the  walls. 

The  Laboratory  is  arranged  on  an  elevated  floor  in  the  centre  of  the  pa- 
vilion; on  white  marble  cased  stone  work  and  on  oak  tables  and  stands  are 
mounted  four  sets  of  apparatus  arranged  for  accurate  determination  of  resistance, 
current  and  potential,  insulation  and  capacity  of  cables;  and  in  addition  a  dark 
room  is  provided  for  including  a  Photometer  and  all  requisite  accessories  for 
measurements  of  light. 

Finally,  outside  the  pavilion  is  a  combined  testing  cart  and  tent,  and  a 
number  of  well  designed  portable  sets  of  apparatus  for  localising  faults  on 
leads  and  testing  their  insulation  resistance. 

The  necessary  current  for  the  various  apparatus,  and  for  the  general 
lighting  throughout  the  pavilion,  which  is  lit  by  both  arc  and  incandescent 


*)  From  The  Electrotechnische  Zeitschrift.    Berlin  1893  No.  42. 


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lamps  is  supplied  from  a  set  of  Pollak  accumulators,  which  are  charged  from 
the  Siemens  &  Halske  five -wire  network  of  mains.  The  lighting  current 
is  kept  constant  by  an  automatic  cell  switch,  also  made  by  the  exhibitors. 


A  well  got  up  catalogue  in  English,  the  cover  ornamented  with  a  drawing  of 
the  statue  we  have  just  described,  serves  as  a  concise  descriptive  <niide  to  the 
various  exhibits  which  are  arranged  in  consecutive  order  round  the  pavilion 


J 


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in 


In  all  some  330  valuable  instruments  in  108  different  types  are  shown; 
these  unquestionably  form  one  of  the  most  interesting  collective  exhibits  of 
apparatus  designed  for  work  in  any  special  branch  of  Science. 


Our  Exhibits  at  Chicago  received  eight  awards. 


IV 


r 

NOTICE. 


1.  We  can  only  consider  claims  made  within  fourteen  days  after  receipt  of  goods. 

2.  All  goods  are   packed  with'  the  greatest  care,   shipping   orders  are   packed  in 
tin  lined  cases,  packing  is  charged  at  cost  price  and  is  not  returnable. 

3.  All  goods  are  sent  at  consignee's  own  risk. 

4.  Orders  from  unknown  correspondents,  or  from  correspondents  who  do  not  fur- 
nish references  will  only  be  accepted  when  accompanied  by  remittance  for  one  third 
of  the  amount  due ;  the  remaining  two  thirds  to  be  paid  upon  despatch  of  the  goods. 

5.  As  alterations  and  improvements  are   constantly  being  made  in  our  apparatus,  the 
illustrations  and  prices  are  liable  to  alteration  without  notice. 

6.  We  use  our  best  endeavours  to  carry  out  repairs  to  any  of  our  apparatus  with  as 
little  delay  as  possible,  chargeing  for  same  at  a  moderate  rate,    if  we   are    unable 
to  quote  a  fixed  price  for  same  beforehand,  which  is  not  always  possible.    Only  under 
exceptional  circumstances  we  can  undertake  the  repair  of  apparatus  not  made  by  us. 

7.  Where    alterations    from    our   standard    patterns    are    required ,    or    special 
instruments  are  made  to  our  customers  specification,  for  which  it  is  impossible  to 
quote  beforehand,    our  charges  for  same  must  be  regarded  as  indisputable,   and 
our  customers  rely  upon  our  basing  them  as  low  as  possible.     We  may  add  that 
we  do  not  like  to  make  single  instruments  to  specification  and  can  but  seldom 
undertake  such  work. 

8.  The  time    stated    for    delivery    is   based   upon  our  usual  factory  routine  and  is 
seldom  exceeded,  tut  is  not  guaranteed;  we  entirely  decline  responsibility  for  losses 
incurred   through   non-delivery    at  time   stated;  whether  arising  from  errors  on  our 
part,  accidents,  or  strikes. 

9.  We  give  the  following  guarantee  with  all  instruments  of  our  manufacture,  namely, 
to  repair  or  replace  free  of  charge  with   new   perfect  instruments,    all    faults    or 
errors  arising  within  one  year  from  date  of  delivery  and  due  to  faulty  material  or 
workmanship.     We  recognise  no  other  compensation  of  any  sort  whatever  and  are 
not  responsible  for  damage    or  loss   in   business   arising  out  of  these  defects.     We 
are,  of  course,  not  responsible  for  accidents,  or  damage  due  to  fair  wear  and  tear, 
unskilled  manipulation  or  from  using  the  instruments  above  their  stated  limits. 

10.   Payment  is  strictly  nett  within  thirty  days,  or  draft  at  one  month  (except 
in  the  case  of  Public  Institutions).    Small  amounts  will  be  collected  by  the  Post  Office 
on  delivery. 
We   especially  request  our  customers  when  ordering1  to  give  the  catalogue 

number  of  each  instrument  required;  unless  this  is  done  we  cannot  be  responsible 

if  the  instruments  do  not  comply  with  their  requirements. 


Postal  Address : 
"HARTMANN  &  BRAUN",  BOCKENHEIM-FRANKFORT  o.  M. 


Telegraphic  Address: 
HARTMANNBRAUN  FRANKFORTMAIN. 

(ONE  word) 

ABC  code  used. 


References  as  to  the  accuracy  and  good  workmanship  of  our  appa- 
ratus are  kindly  permitted  by  the  following  well  known  scientists. 

Dr.  Carl  Barus,  U.  S.  Geological  Survey Washington. 

Dr.  E.  du  Bois-Reymond Berlin. 

Dr.  Borgen,  Imperial  Observatory - Wilhelmshaven. 

Dr.  Ferd.  Brauii Tubingen. 

Dr.  Dietrich Stuttgart. 

Prof.  Galileo  Ferraris Turin. 

G.  Carey  Foster,  Esq.,  B.  A.,  F.  R.  S.  University  College     .     .     .  London. 

Prof.  Frithiof  Holmgren Upsala. 

Dr.  Kittler Darmstadt. 

Dr.  Herm.  I.  Klein,  Astronomer       Cologne. 

Dr.  F.  Kohlrausch Strassburg. 

Dr.  W.  Kohlrausch Hannover. 

Dr.  Neumayer,  Imperial  Observatory Hamburg. 

Dr.  Quincke Heidelberg. 

Dr.  P.  Siloff Warsaw. 

Dr.  W.  H.  Stone,  M.  A.;  F.  R.  C.  P.,  St.  Thomas  Hospital    .     .     .  London. 

Dr.  Strouhal Prague. 

Prof.  N.  Umow Odessa. 

Dr.  A.  von  Waltenhofen Vienna. 

Dr.  H.  F.  Weber Zurich, 


and  many  others  in  all  parts  of  the  world. 


VI 


r 

INDEX. 


The  figures  in  brackets  denote  tlie  patterns  of  tlie  leading  instruments  made  up  to  Spring  of  1804. 

Page 

I.  Apparatus  for  reading  reflecting  Intruments  .........  2 

Telescopes  (396),  Stands  ...................  2—5 

Scales  (957),  Lamps,  Mirror  distance  Indicator       ..........  6 

II.  Galvanometers  ......................  7 

Dead-beat  Galvanometer  with  bell  magnet,  with  Pointer  (455),  with 

Mirror  (268)      ......................  7-13 

Dead-beat  Mirror  and  Pointer  Galvanometer  with  moveable  coil  (105).  .  14—15 
Kohlrausch  pattern  Galvanometer  (I  IB),  Rosenthal  do;  Astatic  do,  and 

Galvanometer  for  Cable  work  (10)   ..............  16—21 

Electrodynamometers  (68),  Tangent  Galvanometers  (71),  Voltameters  (104)  22—26 

III.  Direct-reading  Galvanometers  and  Electrodynamometers      ...  27 
Current  and  Potential  meters,  Wattmeters  for  direct  and  alternating  cur- 

rents (new)       ......................  28-29 

IV.  Standard  copies  of  the   Imperial  Physico-Technical  Laboratory  30 
Standard  Clark  cells,  Standard  Resistances,  Petroleum  baths  (new)       .     .  30—31 
Compensation  Apparatus  (Potentiometers)  for  standard  measurements  of 

the  electrical  quantities  (new)  ................  32—35 

V.  Apparatus  for  determining  Resistances     ...........  36 

Bridges,  Wheatstone-Kirchhoft'  pattern  (161),  Apparatus  for  Electrolytic 

resistances  (236)  .....................  36-37 

Standard  Rheostats,  mounted  in  series  and  decades  for  use  as  branch, 

additional,  and  shunt  Rheostats  (941)   .............  38—43 

Ordinary  Rheostats  mounted  in  series  and  decades  for  use  as  above,  with 

Plug  or  Switch  contacts   ..................  44  —  45 

Bridges  for  high  (  122)  and  low  (40)  resistances,  Thomson's  double  bridge  (new)  46  —  51 
Direct-Reading  Ohmmeter  (new),  Insulation  Testers  (42),  Cable  testing 

cart  (new)    .......................  52—57 

VI.  Apparatus  for  testing  Earth  connections      ..........  58 

Telephone  Bridge,  Lightning  Conductor  Tester  (492),  Simple  Resistance 

meter  (457)       .......    .    .    .............  58-61 

VII.  Accessories  and  Cells  ...................  62 

Single  and  multiple  Switches,  Commutators,  Selectors,  and  Keys     .     .     .  62—65 

Cells,  and  portable  Batteries     .................  66—67 

VIII.  Apparatus  for  Magnetic  measurements     ...........  68 

Bifilar  Magnetometer,  Variometer  (68);  Unifilar  Magnetometer  (130)      .     .  68—73 

Earth  Inductors,  Electromagnets  (large)     .............  74—76 

Bismuth  Spiral  (150),  Apparatus  for  investigating  magnetic  properties  of 

Iron  (new)    .......................  77—79 

IX.  Optical  Apparatus     ....................  80 

True  plane  glass  and  steel  Mirrors,  Eyepieces,  Objectives,  Prisms  .  .  .  80  —  83 

Spectrometer,  Total  Reflectometer,  Cathetometers,  Sphereometers  .  .  .  84—86 
Opal  glass  Photometer,  Standard  Photometer,  Simple  incandescent  lamp 

Photometer  (new)     ....................  87—90 


VII 


r 


X.  Technical  Measuring  Instruments  for  continuous  or  intermittent 

Control  on  electrical  Installations 91 

Standard  Ampere-  and  Voltmeters,  dead-beat,  with  moveable  coil  (197  new)  94—97 
Hotwire  Ammeter  (new)  and  Voltmeter  for  direct  and  alternating  cur- 
rents (553) 98-99 

Spring  Ammeters,  Kohlrausch  pattern  (3919) 100-101 

Electromagnetic  Ammeters  (5198)  and  Voltmeters  (9734) 102-105 

Ammeters  for  medical  purposes  (new) 97  &  105 

Large   size  Central  Station   Voltmeters   for   direct  and  alternating  cur- 
rents (110) 106—107 

Cell  Tester  for  accumulators  (307),  Areometers 97  &  108 

Current  Index  (560),  Magnetic  Field  Explorer 101  &  108 

Electrostatic  Voltmeters  for  high  tensions  (new) 109 

Contact  Voltmeters  (164),  Relays  (239),  Alarm  Voltmeters  (95).     .     .     .  110-113 

Differential  Voltmeter  (new),  Back-Charge  Index  (new) 114  —  116 

Leakage  Index  or  Ohmmeter  (new),  Wattmeter  (new) 117  —  119 

Recording  Ampere-  and  Voltmeters  (90),  Supply  Meters  (new)      .     .     .  120-123 

Galvanoscopes  (1147) 124 

Sketches  of  various  Scales 125-127 

XI.  Switches 128 

Automatic  Switches  for  maximum  and  minimum  current 129 

Automatic  and  Hand-regulating  accumulator  switches,  automatic  Potential 

regulators 130—131 

XII.  Apparatus  and  Material  for  Installation  Work  and  Wiremen  .  132 

Instruments  for  Wiremen,  Insulation  Testers  (425) 132  —  133 

Speed  counter,  with  belt-speed  attachment 134 

Apparatus  for  determining  Cross  section  of,    Fall    of  Potential   in,    and 

Load,  on  any  System  of  Mains,  by  Helberger  (new)     ../-...  135—137 

Wiring  System  and  accessories  for  use  in  wiring  inhabited  rooms    .     .  138—139 

XIII.  Telephone  Stations 140 

XIV.  Small  Dynamos  and  Motors 141 

Portable  Dynamos  for  blasting  purposes 141 

Electromotors,  from  '/»  to  '/«  HP  (111),  Electric  Fans  or  Ventilators     .  142—143 

XV.  Electrical  Thermometry 144 

Pyrometers,  Telethermometers 144 — 147 

XVI.  Electrical  Apparatus  for  Class  Room  purposes  (new) 148 

Galvanometers,  Tangent  Galvanometers,   Bridges,    Ampere-    and  Volt- 
meters, &c .  148  —  152 


The  firm  is  in  posession  of  the  following  German  Patents : 

No.  36554,      No.  36911,      No.  39561,      No.  39869,      No.  51563,      No.  56633,      No.  56696, 

No.  63219,      No.  66678,      No.  68918,      No.  69561,      No.  71484,      No.  74338,      No.  75065, 

No.  75503,     No.  76933,     No.  77576,     No.  78310, 

(in  addition  to  several  applications  already  filed) 

and  a  number  of  foreign  patents. 


VIII 


r 

PREFACE. 


1  his  edition  of  our  catalogue  is  far  larger  than  our  previous  issues.  Our 
endeavours  to  keep  pace  with  all  the  improvements  in  Science  and  Practice, 
and  our  wish  to  facilitate  the  selection  of  the  most  suitable  instrument  for 
whatever  purpose  required,  by  furnishing  a  slight  description  of  the  necessary 
manipulation,  have  led  to  this  increase;  which  we  hope  will  cause  this  catalogue 
to  serve  as  a  book  of  reference  when  using  the  instruments  described. 

With  the  exception  of  the  copies  of  Standards  of  the  Imperial  Physico- 
Technical  Laboratory,  nearly  all  our  instruments  have  been  entirely  designed 
by  our  firm  and  their  associates.  The  usual  standard  types  of  apparatus  have 
been  remodelled  and  improved,  to  bring  them  up  to  the  present  day  requirements 
for  measuring  instruments.  Some  of  Prof.  Kohlrausch's  valuable  designs  have 
also  been  remodelled  in  accordance  with  his  suggestions ;  we  have  always 
made  it  our  special  endeavour  in  improving  and  remodelling  our  instruments, 
to  make  them  as  simple  and  convenient  as  possible,  so  that  they  may  be  used 
by  comparatively  unskilled  hands  without  loss  of  time;  and  for  this  reason  we 
have  originated  several  direct  reading  instruments,  to  which  we  would 
especially  draw  the  attention  of  all  practical  engineers. 

Especial  care  is  given  to  the  calibration,  adjustment  and  exact  deter- 
mination of  Constants,  for  which  purpose  we  have  a  very  complete  and 
carefully  designed  plant,  comprising  4  Dynamos  for  direct  currents  up  to  1500 
amperes,  three  sets  of  large  accumulators  and  one  set  of  several  hundred  small 
ones  also  capable  of  discharging  at  the  rate  of  2000  amperes  and  at  potentials 
up  to  800  volts,  in  addition  to  a  direct  current  motor  transformer  for  potentials 
up  to  2000  volts  and  electrostatic  arrangements  for  higher  potentials.  For 
alternating  current  work  within  very  wide  limits,  an  alternating  current 
dynamo  with  3  transformers  having  a  range  up  to  1000  amps  and  10000  volts 
is  employed. 

Whilst  using  our  very  best  endeavours  to  meet  all  the  requirements  of 
accuracy,  convenience,  and  mechanical  perfection  in  design,  it  will  still  sometimes 
occur  that  every  day  use  of  our  instruments  will  suggest  points  in  which 
improvements  are  possible;  and  we  shall  be  extremely  obliged  for  any  such 
suggestions. 


V. 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


I. 

Apparatus  for  use  in  reading  Reflecting 
Instruments. 

Reading  Telescopes. 

Large  Size  Telescopes,  fully  mounted,  in  well  designed  massive 
framework;  absolutely  without  iron.  Telescope  with  powerful  objective, 
Steinheil  eye-piece,  rack  and  pinion  adjustment  to  do,  which  is  available 
down  to  1  metre  distance  from  the  object;  vertical  and  horizontal  micro- 
meter adjustments.  Angle  of  elevation  50—60°. 

Scale  holder  for  use  with  wood  or  glass  scales,  adjustable  for  height 
and  fitted  with  swivel  arrangement  for  use  with  upright  scale. 

To  facilitate  accurate  adjustment  on  to  the  mirror,  the  upper  part 
of  the  instrument  is  adjustable  by  means  of  rack  and  pinion  for  00—75  mm 
from  the  tripod  base,  which  is  fitted  with  levelling  screws. 


No. 

TELES 
Aperture 

SCOPE 
Focus 

M  a  g  n  i  f  i  e  s 

PRICE 

355 

30  mm 

25cm 

18  times 

M.  330.— 

356*) 

40  mm 

32cm 

24  times 

M.  440.— 

357 

55  mm 

55  cm 

30  times 

M.  550.- 

If  required  fitted  with  Euryscopic  Micrometer  Eye-piece    Extra  M.  15.  —  . 

EXTRAS. 

1)  Level  for  use  on  the  horizontal  plane  of  telescope   thus  enabling  the 
instrument  to   be  used  to   determine  the  meridian,   by  corresponding 
readings  on  a  star M.  25. — 

2)  Circular  level,  fitted  on  the  base  of  the  telescope  support     M.  16.— 

3)  Diaphragms  fitted  to  cover,   to  reduce  the  aperture   of  the  objective 

M.  12.— 

4)  Steinheil  Eye-pieces,  various  powers,  interchangeable,  each  M.  15. — 

5)  Euryscopic    Micrometer    Eye-pieces,     Mittenzwey    type,     each 

M.  30.— 

6)  Adjustable  Prisms,  Neumeyer  type,  for  use  in  front  of  the  objective, 
to  read  two   or  three  instruments   from   one  spot,   with   the  requisite 
scale  holders;  made  only  for  No.  357 each  M.  150. — 


*)  The  most  convenient  size. 


J 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  356. 

Reading  Telescope  for  use  with  Reflecting 
Instruments. 

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HARTMANN  &  BRAUN,  BOCKENIIEIM- FRANKFORT  o.  M. 


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HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 

^ —  *ei^ =  <-~ 


Reading  Telescopes,  not  mounted. 

No.  350.  Reading  Telescope, 

aperture  of  objective  10  mm,  focus 
6  or  9  cm,  with  Ramsden  eye- 
piece, equiv.-focus  1  cm,  sliding  [|  i/16  n   Qr 
adjustment  to  eye-piece.  M.  25. — 

No.  351.  Reading  Telescope, 
aperture  15  mm,  focus  9  or  12  cm, 
with  Ramsden  eye-piece,  equiv.- 
focus  1  or  1.25  cm  with  sliding 
adjustment  to  eye-piece  M.  36. — 

No.  351  a.  As  above,  but  with 
rack  £  pinion  adjustment  M.45. — 

No.  352.  Reading  Telescope, 
aperture  27  mm,  focus  18,  21  or 
25  cm,  with  Ramsden  eye-piece 
equiv.-focus  either  1,  1.25,  1.5  or 
2  cm,  with  sliding  adjustment 
to  eye-piece  .  M.  50. — 

No.  352 a.  As  above,  but  with 
rack  £  pinion  adjustment  M.60. — 

No.  353.  Reading  Telescope, 
aperture  30  mm,  focus  25  or  32  cm , 
with  Steinheil  eye-piece  equiv.- 
focus  1.5  or  2  cm,  and  rack  and 
pinion  adjustment  to  do  M.  75. — 

No.  354.  Reading  Telescope, 
aperture  40  mm ,  focus  32  or  40  cm , 
with  Steinheil  eye-piece  equiv.- 
focus  1.5  or  2  cm;  and  rack  and 
pinion  adjustment  to  do  M.  100.— 

Any  of  these  telescopes  can  be  fitted 
with  euryscopic  micrometer  eye- 
pieces at  an  extra  cost  of  M.  15.— 

Stands. 

No.  348.  Plain  Stand,  height  175  cm,  in  light  wood,  with  metal 
sliding  clamp  and  hinge  for  use  with  any  of  the  above  telescopes,  and  scale 
holder.  Price  M.  70.— 

No.  348 a.  As  above,  but  with  metal  sliding  clamp  and  micrometer 
adjustment  to  telescope  in  both  planes,  with  scale  holder  .  .  M.  125. — 

No.  349.  Gauss  Stand.  Legs  in  solid  oak  with  triangular  section 
rising  bar  in  light  wood  oak  veneered  to  match;  strong  wood  clamping 
screws,  size  of  table  35  cm.  Price  M.  55. — 

No.  349  a.     As  above,  for  larger  instruments,  size  of  table  50  cm. 

Price  M.  75. — 

Arrangement    for    fixing  reading   telescopes   on    a   cross    bar.   - 
The  price  varying  in  accordance  with  the  mounting  required,  we  can  only 
quote  on  receipt  of  particulars. 


J 


0  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Scales. 

No.  360.    Wood  Scales  of  T  section,  made  of  well  seasoned  material 
with  narrow  paper  strips,  machine  divided  at  our  works,  with  mirror  figures. 

No.  360  a.   Transparent  Celluloid  Scales,  with  one  edge  mounted 
in  wood  bar,  for  use  with  reading  lamp. 
Length  in  cm 

,,T      ,11  division  =  2  mm*)   M. 
Wood  |  .  1 

I  -1        »  »          <> 

Celluloid    1  =  1 


40       60    i    80    !  100 


5.- I   7.-J  9.- 1 11.- 
6.-  !  8.-  1 10.- !  12.- 


9.-  1 12.- 1 16.- 1 21.- 


*)  Most  suitable  for  use  with  low  power  telescopes. 

No.  361  and  361  a.  Scales  on  plate  and  opal  glass.  The  glass 
strips  for  these  scales  are  specially  prepared,  ground  and  polished  true 
on  both  surfaces,  with  finely  etched  millimeter  divisions  and  mirror  figures. 


Length  in  cm. 
Plate  glass 
Opal  glass  . 


M. 


40 

60 

80 

100 

120 

140 

15.- 

20.- 

25.- 

30.-  j  36.- 

42.- 

16.- 

21.- 

27.- 

35.- 

45.- 

55.- 

We  shall  be  pleased  to  supply  these  scales  to  any  length  or  pattern,  with  con- 
secutive  marking,  or  scaled  from  the  centre;  also  scaled  for  direct  readings.  If 
desired  the  plate  glass  scales  can  be  supplied  on  finely  ground  glass,  thus  enabling 
the  graduations  to  be  illuminated  from  the  back,  or  for  use  as  direct  reading. 

Our  opal  glass  scales  have  on  account  of  their  brilliancy  been  adopted  by  a  great 
number  of  laboratories.  Several  hundreds  are  in  use. 


'/8  n.  Gr. 


No.  362a. 


Wood  case,  plain  or  polished,  for  glass  scales. 
Price  according  to  length.  From  M.  8. —  to  M.  20. — 

Tubular  Gas  Rod,  in  brass,  with  cock  and  steatite 
burners  to  illuminate  the  scale  by  a  number  of  small 
gas  jets.  Price  M.  10. — 

No.  362.  Lantern  in  sheet  copper, 
with  slot  or  diaphragms,  adjustable  con- 
vex lens,  and  scale -holder.  Fitted  either 
with  gas,  petroleum,  or  incandescent  lamp, 
on  wood  tripod  stand.  Price  M.  85.— 

No.  362 a.  As  above,  but  adjustable 
for  height,  with  metal  tripod  stand. 

Price  M.  125.— 

No.  363.  Mirror  Distance  Indicator. 
This  consists  of  maple  rod  divided  in  centi- 
metres, which  can  be  extended  to  4  metres, 
having  a  fixed  contact  for  the  scale  end 
and  an  ivory  contact  with  micrometer  ad- 
justment for  use  on  the  mirror;  a  suitable 
stand  provides  a  means  of  fixing  the  ex- 
tended rod  in  any  desired  position. 
Price  M.  200.—,  without  stand  M.  160.— 


X-u 


(0  HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


II. 

Galvanometers. 

In  addition  to  certain  special  types,  the  following  galvanometers  (for  small  currents) 
may  be  divided  into  three  classes;  namely,  galvanometers  with  bell  (thimble)  magnet; 
with  moveable  coil;  and  with  astatic  magnets. 

In  designing  these  galvanometers  the  chief  points  we  have  kept  before  us  are, 
that  they  shall  be  portable,  easily  and  quickly  adjusted,  practically  dead-beat  and  of 
the  highest  attainable  degree  of  sensitiveness;  the  sensitiveness  given  for  each  instrument 
shows  that  we  have  carried  out  this  last  stipulation  in  a  very  high  degree. 

In  galvanometers  of  the  first  class  we  have  attained  this  by  flattening  the  copper 
damper,  thus  enabling  the  winding  to  be  brought  close  up  to  the  bell  magnet,  which 
we  have  also  made  smaller  than  formerly  and  are  thus  enabled  to  increase  the  number 
of  turns  in  the  coil.  Great  care  is  taken  in  the  manufacture  of  the  modified  type  of 
Siemens  bell  magnet;  they  will  carry  50—75  times  their  own  weight,  and  therefore 
cause  a  powerful  damping  action  although  they  have  ample  play  in  the  damping  case. 

The  second  class  is  noticeable  for  their  powerful,  homogeneous  magnetic  field, 
thus  rendering  them  unaffected  in  the  proximity  of  other  magnetic  fields,  and  for  their 
extremely  even  scale  through  wide  limits. 

In  the  third  class  the  suspension  fibres  are,  as  far  as  practicable,  quarz  filaments. 

In  all  the  various  designs  great  care  has  been  taken  to  protect  the  moving  parts 
from  air  currents.  The  mirror  galvanometers  are  mounted  with  true  plane  mirrors, 
accurately  surfaced,  and  silvered  at  back,  which  are  clamped  as  lightly  as  possible  in 
three  claws;  this  method  of  suspension  entirely  obviates  the  annoyance  caused  by  the 
deformation  of  mirror.  The  mirror  framework  is  adjustable  as  regards  the  magnet,  the 
instruments  can  therefore  be  read  at  any  azimuth.  The  front  of  mirror  case  is  fitted 
with  a  true  plane  glass  aperture  canted  slightly  forward,  thereby  obviating  reflections. 


No.  366.  Simple  dead-beat  Galvanometer  with  pointer,  powerfully 
damped  bell  magnet  on  cocoon  fibre  suspension.  Coils  wound  with  two 
separate  wires  in  parallel.  All  parts 
are  plainly  visible  within  the  round 
wooden  case  which  can  be  turned  on 
the  metal  tripod  stand.  A  safety  catch 
is  provided  to  control  the  swing  of  the 
pointer  and  for  travelling  purposes. 

Made  in  two  patterns: 

I.  Low  Resistance.   2  —  5  ohms. 
The  coil  windings   attached  to  three  J 
terminals  so  that  each  coil  can  be  used  i 
separately,  or  both  in  series  as  well 
as  differentially. 

Sensitiveness:  1°  on  scale  =  0.00005  ampere.  Price  M.  90.  — 

II.  High  Resistance.    With  any  desired  resistance  up  to  1000  ohms. 
The  coil  windings  attached  to  four  terminals,  so  that  the  instrument  can 
be  used  as  differential  galvanometer  or  the  windings   can  be  coupled   in 
parallel  thus  reducing  the  resistance  to  1/4. 

Sensitiveness  at  1000  ohms:  1°  on  scale  =  0.000005   ampere. 

Price  M.  100.— 


I 

r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  Q 

^      -^   ^^ 

No.  367. 
Dead-beat  Differential-Galvanometer. 


V*  n.  Gr. 


No.  367.  Dead-beat  Differential-Galvanometer  with  index  pointer 
reading  on  German  silver  engraved  scale  with  mirror  underneath  to  ob- 
viate parallax  errors.  Bell  magnet  on  raw  silk  fibre  suspension  working 
in  a  shallow  but  very  powerful  copper  damper;  means  are  provided  to 
control  the  swing  of  the  pointer,  and  to  render  the  instrument  portable. 
A  circular  level  is  provided  for  adjustment  and  the  galvanometer  is  mounted 
to  turn  and  be  clamped  in  any  position  on  the  circular  wood  base  which 
is  fitted  with  levelling  screws.  The  coils  are  removeable  and  inter- 
changeable without  dismounting  the  instrument  and  are  adjustable  to  some 
extent  as  regards  the  magnet,  thus  affording  a  means  of  modifying  the 
sensitiveness,  or  for  accurate  adjustment  when  used  as  a  differential  gal- 
vanometer; they  are  double  wound  with  two  wires  of  the  same  resistance, 
which  can  therefore  be  varied  from  one  to  sixteen  times. 

An  adjustable  directive  magnet  can  be  used  on  one  side  to  render 
the  instrument  astatic  and  so  increase  the  sensitiveness. 

Sensitiveness,  with  the  coils  usually  supplied  of  about  100  ohms, 
1°  on  scale  '•*  0.000008  amp.;  if  astatic  —  0.000002  amp.  Price  M.  200.— 

Pair  of  coils,  Voller's  system,  for  measuring  the  resistance  of  in- 
candescent carbon  loops;  with  a  resistance  ratio  of  1  :  20  (0.5  and  10  ohms) 
with  screw  arrangement  to  adjust  the  thick  wire  coil  as  regards  the 
magnet  for  exact  differential  working.  Price  M.  60.— 

Coils,  of  various  windings,  interchangeable  with  those  supplied  (see 
next  page). 


r 


-  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 

.«O  QJ 


No.  367a.     Portable  Dead-beat  Galvanometer 
with  Telescope. 


No.  367a.  Portable  Dead-beat  reflecting  Galvanometer  with 
Telescope.  The  general  arrangement  of  this  instrument  is  the  same  as 
in  the  Differential-Galvanometer  No.  367.  The  telescope*)  has  an  aperture 
of  10  mm,  focus  6  cm,  thus  giving  ample  magnifying  power  with  great 
brilliancy;  it  is  mounted  on  a  counterbalanced  arm  and  can  be  turned 
independantly  of  the  galvanometer.  The  mirror  is  adjustable  as  regards 
the  magnet.  To  enable  the  winding  to  be  easily  adjusted  to  the  magnetic 
meridian  a  pole  indicator  to  the  magnet  is  mounted  above  the  mirror. 
Stop,  level,  and  magnet  for  astatic  work,  same  as  in  No.  367.  The 
instrument  is  suitable  for  either  laboratory,  workshop,  or  outdoor  use 
and  sufficiently  sensitive  for  most  galvanometric  measurements. 

Sensitiveness,  not  astatic,  using  the  coils  of  about  100  ohms  supplied 
with  the  instrument:  1mm  deflection  on  scale  at  25  cm  distance =0.000 000 9 
amp.;  with  coils  of  4000  ohms  =  0,0000003  amp.  Price  M.  285.- 

Magnet  arrangement  for  astatic  work,  as  in  No.  372.  Price  M.  40. — 

Coils,  of  various  windings  interchangeable  for  this  instrument,  or 
No.  367  of  any  desired  resistance  up  to 

a  total  resistance  of  1000  ohms  per  pair  Price  M.  40. — 

,      „  n          „   2000      „        „       „         „       „    50.- 

..   4000  ,    60.— 


*)  If  the  telescope  and  counterbalanced  arm  are  not  required,  deduct   .     M.  70.— 


r 

,  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  371  and  371a. 
Dead-beat  reflecting  Galvanometer. 

In  this  design  we  have  combined  all  the  advantages  of  the  Siemens' 
bell  magnet,  the  Wiedemann  adjustable  coils,  and  Braun's  method  of 
astatization  by  means  of  a  soft  iron  ring,  with  several  mechanical 
improvements. 

By  reducing  the  size  of  the  bell  magnet  and  the  sectional  area 
of  the  copper  damper  whilst  retaining  all  its  former  damping  power, 
and  suspending  the  damper  on  comparatively  thin  wires,  we  have  succeeded 
in  bringing  the  winding  so  close  round  the  poles  of  the  magnet,  that  the 
instrument  is  now  ten  times  as  sensitive  as  formerly.  The  iron  ring  is 
in  two  parts,  this  arrangement  allows  their  adjustment  relatively  to  each 
other  and  therefore  should  any  polarity  arise  in  the  ring,  it  can  be  easily 
eliminated,  whilst  it  is  easily  removeable  if  not  required. 

The  coils  are  double  wound  with  silk  covered  wires,  the  windings 
can  therefore  be  coupled  up  so  that  the  resistance  varies  as  desired  from 
either  unity  to  two,  four,  eight,  or  sixteen  fold.  The  total  resistance  of 
the  coils  supplied  with  this  galvanometer  is  about  400  ohms;  they  are, 
of  course,  interchangeable  with  similar  coils  of  various  resistances.  Each 
coil  has,  in  addition,  some  turns  of  thick  wire. 

A  circular  level  is  mounted  on  the  tripod  stand  to  facilitate  the  use 
of  the  instrument. 


No.  371.  Dead-beat  reflecting  Galvanometer.  Large  size.  Can 
be  turned  and  clamped  in  any  desired  position,  mounted  on  heavy  metal 
tripod  base.  Movement  of  coil  controlled  by  rack  and  pinion;  the  coil 
bar  divided  into  millimetres. 

Sensitiveness  with  coil  coupled  in  series,  400  ohms  resistance,  and 
without  the  use  of  the  iron  ring  for  astatization:  1  mm  deflection  on  the 
scale  at  1  m  distance  =  0.00000008  amp.  Price  M.  520.— 


10 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  371. 
Dead-beat  reflecting  Galvanometer.    Large  size. 


.J 


11 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.STla.  Simple  Dead-beat  reflecting  Galvanometer. 


No.  371a.  Simple  Dead-beat  reflecting  Galvanometer,  resembling 
No.  371  throughout,  but  simplified  in  the  details;  i.  e.  with  wood  base, 
sliding  adjustment  to  coils,  and  the  coil  bar  divided  in  half  centimetres. 

Sensitiveness,  approximately  the  same  as  No.  371.     Price  M.  390. — 

Coils,  of  various  windings,  double  wound,  interchangeable  for  this 
instrument  or  No.  371,  with  a  total  resistance  of  about  1000,  2000,  or 

5000  ohms per  pair  M.  70.—,  80.-  or  M.  90.— 

as  above,  but  of  extremely  low  resistance,  for  thermal  currents  M.  55.— 

or  with  winding  insulated  by  gutta  percha  for  frictional  electricity  M.  50.— 

Prices  for  any  desired  winding  on  application. 

Control  Magnet  (Hauy's  rod)  for  astatization,  mounted  on  suspension 
tube  with  requisite  adjustments  for  rotation  and  extension.  Preis  M.  25. — 

In  both  of  these  instruments  the  Wiedemaim  ring-magnet  with  suitable  damper 
will  be  supplied  instead  of  the  Siemens'  bell  magnet,  without  extra  cost,  if  desired. 

A  very  convenient  arrangement,  enabling  either  type  of  magnet  to  be  used  and 
quickly  changed,  can  be  supplied  at  an  extra  cost  of M.  50.— 


0  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  Q 


No.  373. 
Lecture-Room  Galvanometer. 


n.  Gr. 


No.  373.  Lecture-Room  Galvanometer,  with  very  light  pointer 
visible  at  long  distances  against  a  scale  of  white  lines  on  a  black  ground. 

Bell  magnet  on  raw  silk  fibre  suspension,  strongly  damped  by 
suspension  in  narrow  copper  core.  Coils  with  a  total  resistance  of  about 
10  ohms,  are  slightly  adjustable  as  regards  the  magnet;  all  working  parts 
under  glass;  the  various  windings  on  coils  are  brought  out  on  to  a  separate 
plug  switch  and  can  thereby  be  coupled  either  in  series,  in  parallel  or 
differentially.  The  scale  can  always  be  arranged  to  face  the  audience, 
as  the  instrument  can  be  turned  on  its  stand  and  the  pointer*)  easily  ad- 
justed as  regards  the  magnet. 

Sensitiveness:  1  Space  (=5  degrees)  —  0.000 15  amp.    Price  M.  230.- 

Thimble  magnet,  with  true  plane  mirror  and  mirror  case,  fitted 
with  accurately  surfaced  glass  front;  for  use  for  exact  measurements. 

Sensitiveness:  1  mm  deflection  on  scale  1  m  distant  =  0.000 000 5  amp. 

Price  M.  40.— 

Coils,  of  various  windings,   for  use   in  lieu   of  those  supplied,   with 
resistance  of  about  1,  400,  10UO,  2000,  or  4000  ohms. 
Price  per  pair  M.  30.—,  35.—,  40.—,  50.—  or  M.  60.— 

*)  When  adjusting  the  pointer  as  regards  the  magnet,  the  milled  disc  above 
same  should  be  held  between  two  fingers  of  one  hand  and  the  carriage  carrying 
the  pointer  between  two  fingers  of  the  other  hand;  it  is  of  course  adviseable  not  to 
put  any  strain  on  the  silk  fibre  whilst  this  is  being  done. 


13 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.* 


Deat-beat  Galvanometers  with  suspended 
moveable  coil. 

Deprez-d'Arson  val    System    (arrangement  of  details   patented). 


No.  535a.  v*  n.  Gr. 


These  instruments  have  been  improved  against  the  original  type  of 
suspended  coil  galvanometers  of  Deprez  and  d'Arsonval.  A  number 
of  powerful  magnets  with  common  pole  pieces  produce  a  very  strong  and 
at  the  same  time  homogeneous  field  throughout  the  entire  range  of  the 
moveable  coil.  The  fram  upon  which  the  moveable  coil  is  wound,  is  of 
aluminium  and  works  in  an  extremely  narrow  clearance  space,  thus 
attaining  perfect  aperiodicity,  independent  of  the  outer  circuit,  and  an  extreme 
sensitiveness.  The  coil  is  suspended  either  between  very  thin  wires 
which  act  in  opposition  to  the  current,  and  are  taking  at  the  same  time  the 
current  to  the  coil,  or  —  convenient  for  certain  purposes  •—  on  a  raw 
silk  fibre  in  which  case  a  two-way  spring  acts  as  counter  force,  or  finally 
on  a  quarz  fibre.  In  the  two  latter  cases  the  current  is  taken  to  the  coil 
through  excessively  thin  strips  of  silver  foil  which  have  only  an  inappre- 
ciable effect  on  its  movement.  Owing  to  their  extremely  powerful  magnetic 
field  these  galvanometers  are  unaffected  by  the  earth  magnetism  or  by 
other  extraneous  magnetic  influences  and  can  therefore  be  used  in  proximity 
to  dynamos.  They  ace  also  less  sensible  against  vibrations.*)  Their  pro- 
portional deflections  render  them  serviceable  for  a  great  many  applications. 


*)  If  the  pointer  galvanometer  No.  535  as  well  as  even  the  mirror  galvanometer 
No.  535a  ar  to  be  used  on  places  which  are  relatively  contineously  shaked  (workshops, 
engine  houses  &c.)  the  coil  can  be  fitted  with  a  glycerin  damper.  Price  M.  35.— 

I 

14 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  0 


No.  535.  Suspended  moveable  coil  Galvanometer,  easily  set  up 
and  adjusted  by  levelling  screws  in  base  and  circular  level;  is  safely 
portable,  as  the  glass  case  is  firmly  fastened  and  a  travelling  stop 
is  provided  which,  in  one  movement,  slackens  the  fibre  suspension  and 
clamps  the  moveable  coil;  this  stop  is  under  the  small  glass  bell, 
which  is  mounted  on  the  outside  case  by  a  bayonet  joint,  to  render  it 
accessible.  The  galvanometer  is  read  by  means  of  a  pointer  moving 
over  an  arc  divided  in  degrees;  a  mirror  to  eliminate  parallax  errors  is 
mounted  underneath  same. 

Sensitiveness:  resistance  of  coil  usually  supplied  about  50  ohms. 
1°  deflection  =  0.000002  amp.  Price  M.  200.— 

No.  535  a.  A  similar  instrument  as  above,  but  arranged  as 
reflecting  galvanometer.  The  true  plane  reflecting  mirror  or,  if  preferred, 
a  light  concave  mirror  is  frictionally  held  in  an  aluminium  framework  mounted 
on  the  moveable  coil.  The  glass  bell  has  a  sight  aperture  in  it  covered 
by  an  accurately  surfaced  glass  which  is  canted  slightly  forward. 

Sensitiveness:  resistance  of  coil  about  2000  ohms.  1  mm  deflection 
on  scale  1  m  distant  ==  0.00000002  amp.  Price  M.  230.— 

Mirror  casing:  with  small  reading-  telescope  the  axis  of  which  forms  with  the  plane  of  mirror  an  angle 
of  about  45°  so  that  the  deflection  of  same  may  be  observed  at  any  mark  or  scale  properly  placed  at  any  desired  distance. 
(See  left  hand  figure  below.)  Price  M.  5O.— 

Price  instead  of  ordinary  mirror  case  M.  4O. — 

No.535or535a  if  wound  as  Differential-Galvanometer  Extra  M.  40. — 
No.  535a  if  constructed  as  Ballistic  Galvanometer  .  „  „  20.— 
A  second  winding  to  the  latter  to  steady  same  .  .  „  „  60. — 


to  No.  535 a. 


An.Gr. 


No.  536 


in.GP. 


No.  536.  Simple  moveable  coil  Galvanometer,  with  coil  on  steel 
pivots  in  jewelled  centres,  with  travelling  stop,  very  portable,  and  ready 
for  use  without  further  adjustments.  Pointer  reading  on  paper  scale 
divided  in  degrees.  Brass  case  and  wood  base. 

Sensitiveness:  coil  of  about  50  ohms.  1°= 0.000  025  amp.  Price  M. 135.— 

No.  536  a.      Similar    instrument    as   above,    but   with    only    three 

magnets  instead  of  six ;  is  not  quite  as  high,  and  therefore  still  more  portable. 

Sensitiveness:  coil  of  about  10  ohms.  1°  =  0.000  05  amp.  Price  M.100.- 

For  instruments  of  similar  design,  but  for  use  with  large  currents, 
see  No.  530,  p.  28,  and  No.  601,  p.  92. 


15 


r 

0  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  c 

c-O  ^jjy 

No.  368. 
Kohlrausch  Mirror  Galvanometer. 


^ 


U — Vu  n.  Gr. 


No.  368.  Kohlrausch  Mirror  Galvanometer,  with  undivided  oval 
coil  in  the  interior  of  which  the  magnet,  a  steel  mirror,  is  suspended  on 
a  silk  fibre.  The  damping  can  be  adjusted  within  wide  limits  by  moving 
the  copper  core.  The  coil  has  both  thick  and  thin  windings,  each 
of  which  is  composed  of  two  wires  of  equal  resistance  wound  side  by 
side;  the  instrument  can  therefore  be  used  as  differential  galvanometer. 
To  eliminate  thermo  currents  these  windings  end  in  copper  terminals. 

The  various  ways  in  which  the  circuits  may  be  connected  and  the 
use  of  an  adjustable  control  magnet  which  is  fixed  underneath  the  stand 
enable  the  sensitiveness  to  be  varied  as  desired. 

Sensitiveness  with  a  resistance  of  about  50  ohms  and  not  astatic: 
1  mm  deflection  on  scale  1  m  distant  =  0.000  0004  amp. 

With  Stand  and  control  magnet Price  M.  200. — 

Without  Stand „       „     180.— 

If  the  steel  mirror  is  polished  on  both  sides  so  that  readings  can 
be  taken  from  either  East  or  West Extra  M.  25.— 

Guard  Ring,  in  soft  Swedish  iron,  rendering  the  galvanometer  more 
independent  of  iron  in  the  neighbourhood  or  other  influences,  and  at  the 
same  time  considerably  increasing  the  sensitiveness.  Price  M.  25. — 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  369.  Rosenthal  Micro-Galvanometer.  In  lieu  of  the  horseshoe 
shaped  magnet  with  hooked  ends  and  vertical  suspension  as  suggested 
by  Rosenthal,  we  employ  in  this  instrument  a  somewhat  Z  shaped  magnet 
with  mirror,  which  is  rendered  astatic  by  the  Ferrini  process  in  which 
similar  poles  are  produced  at  both  ends  of  the  magnet.  The  poles  project 
within  the  coils.  The  Rosenthal  arrangement  gives  extreme  sensitiveness 
for  a  minimum  amount  of  wire  employed,  and,  in  combination  with  the 
Topler  air  damper,  furnishes  a  galvanometer  which  is  most  suitable  for 
thermo-currents  or  for  physiological  purposes.  Price  M.  300.— 


No.  370. 

Astatic   Mirror    Galvano- 
meter. 

No.  370.  Astatic  Mirror  Gal- 
vanometer with  compound  magnets 
made  up  of  thin  laminae  and  each 
surrounded  by  a  coil.  Adjustable 
copper  sheath  to  control  damping 
action,  adjustable  mirror;  mounted 
on  marble  base  to  turn  in  metal 
tripod  stand.  All  parts  are  easily 
accessible  on  removal  of  the  circular 
glass  cover. 

Sensitiveness:  with  a  total  re- 
sistance of  about  10  ohms  and  with 
a  10  seconds  oscillation —  0.00000015 
amp.  for  a  1  mm  deflection  on  scale 
1  m  distant.  Price  M.  280.— 


4  n.  Gr. 


0  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  370a. 
Astatic  Mirror  Galvanometer  for  ballistic  work. 


No.  370  a.  Astatic  Mirror  Gal- 
vanometer for  ballistic  work  with  inter- 
changeable tubular  magnets,  40  mm  long, 
and  adjustable  mirror;  the  magnet  carriage 
is  of  aluminium  and  can  be  introduced 
into  the  coil  from  the  outside.  The  coil 
is  double  wound  with  two  similar  wires 
side  by  side  and  another  coil  of  any  other 
winding  can  be  used  in  its  place.  The 
damping  action  is  controlled  by  an  ad- 
justable copper  sheath,  which  can  be 
entirely  removed,  if  desired.  All  parts 
are  easily  accessible  after  the  strong 
glass  cover  is  removed.  The  complete 
galvanometer  can  be  turned  in  its  metal 
stand. 

Sensitiveness  with  a  resistance  of 
50  ohms  and  a  15  seconds  oscillation: 
1  mm  deflection  on  scale  1  m  distant 
=  0.00000002  amp.  Price  M.  350.— 

Interchangeable  Coils,  of  any  de- 
sired winding  up  to  1000  ohms. 

Price  M.  50.— 


J 


IB 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  370b. 
Large  Astatic  Mirror  Galvanometer. 

Weber  type. 


No.  370b. 

Astatic  Mirror  Galvano- 
meter Weber  type,  with 
all  modern  improvements. 
Tubular  magnets  easily  in- 
serted and  interchangeable, 
120  mm  long,  mirror  ad- 
justable. The  coil  is 
double  wound,  but  not 
interchangeable;  adjustable 
copper  damper.  This  in- 
strument, which  is  of  extre- 
mely good  design,  is  in  all 
other  respects  similar  to 
No.  370a,with  the  exception 
that  the  glass  cover  is  oval 
in  shape  and  that  the  wor- 
king parts  are  mounted 
direct  on  the  base, 
and  cannot  therefore 
be  turned  in  same. 

It  is  identical  with 
the  Galvanometer  No. 
427  p.  74  for  use  with 
the  Weber  Earth -In- 
ductors. 

Price  M.  400.- 


T 


_  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  _ 

^Q_  _          C)^ 

No.  372. 
Astatic  Dead-beat  Mirror  Galvanometer. 


No.  372.     Astatic  and  Dead- 
beat  Mirror  Galvanometer.    In 

this  instrument  the  magnet-system 
is  in  the  form  of  two  hollow  semi- 
cylinders  coupled  together  and  sus- 
pended vertically,  thus  rendering 
the  system  highly  astatic,  whilst 
retaining  all  the  advantages  of  the 
bell  magnet.  The  system  is  sus- 
pended on  either  quarz  or  raw 
silk  fibre,  the  mirror  is  adjustable 
and  encased  in  the  centre  of  the 
instrument,  the  casing  can  be 
removed  if  required.  The  copper 
damping  action  is  adjustable.  Two 
pairs  of  coils  with  a  total  resistance 
of  either  5000  or  10000  ohms;  two 
control  magnets  which  can  be 
turned  and  adjusted  as  required, 
are  especially  useful  to  control  the 
period  of  oscillation  of  the  instru- 
ment. Ebonite  pillars  are  provided 
underneath  the  levelling  screws 
on  the  base. 

Sensitiveness:  with  10  seconds 
oscillation  and  resistance    of  5000 
ohms:    1   mm    deflection    on  scale 
1  m  distant  ==  0.0000000025  amp. 
Price  M.  550.— 


Interchangeable  coils,*) 
two  pairs  of  any  desired 
lower  resistance. 

Price  M.  150.— 


Extremely  light  mag- 
net-system, on  the  same 
principle  as  above  but  using 
very  thin  rods  in  lieu  of  the  semi  tubular  magnets,  for  use  for  the 
highest  sensitiveness.  Price  M.  30. — 

Instead  of  the  magnet-system  above  described,  Lord  Kelvin's  pattern 
will  be  supplied,  if  desired,  without  extra  cost. 

*)  If  required  these  coils  can  be   supplied  wound   with   wire  gradually  increasing 
in  size  from  the  centre  outwards. 


20 


^  HARTMANN  &  BRAUN,  BOCKENHETM- FRANKFORT  o.  M.  ^ 

,-0 f$gyi ~  Cx-> 

No.  372  a. 

Astatic  Galvanometer  for  cable-work  with 
reading  telescope. 


No.   372  a.     Portable    Astatic    Galvanometer    for    cable -work. 

Similar  in  design  to  No.  372  but  with  short  silk  fibre  suspension  and 
fitted  with  telescope  carried  on  a  balanced  arm  which  can  be  turned 
round  the  stand.  The  small  telescope  is  mounted  about  50  cm  away 
from  the  mirror  and  has  an  adjustable  scale  attached.  To  render  the 
instrument  as  portable  as  possible  the  telescope  arm  is  hinged  to  enable 
it  to  be  folded  upwards  as  shown  by  the  dotted  lines;  and  a  travelling 
stop  is  fitted  to  the  magnet  system.  A  circular  level  facilitates  quick 
adjustment  and  the  instrument  is  extremely  serviceable  wherever  portability 
is  required  as  for  instance  for  use  in  a  cable  testing  cart. 

Sensitiveness:  approximately  the  same  as  No.  372.     Price  M.  650.— 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  378. 
Unifilar-Electrodynamometer  for   small  currents. 

Kohlrausch  type. 

No.  378.  The  Mirror  reading  Electrodynamometer  by  Kohl- 
rausch is  especially  intended  for  use  instead  of  galvanometers  when 
measuring  the  resistance  of  electrolytes,  for  which  purpose  it  is  more 
portable  and  easier  to  erect.  Galvanometers  with  bifilar  suspension  are 
not  sufficiently  sensitive  for  many  purposes,  if  the  fibre  suspensions  are 
fairly  far  apart,  whilst  if  brought  close  together  they  are  awkward  to 
suspend  properly  and  are  as  a  rule  insecurely  mounted.  In  this  instrument 
the  inner  moveable  coil  is  hung  on  one  wire  only  which  serves  at  the 
same  time  to  carry  the  current  to  the  coil,  the  other  lead  underneath 
being  either  an  extremely  fine  silver  foil  strip,  or,  if  for  alternating  current, 
a  platinised  platinum  electrode  which  dips  into  a  small  glass  receiver 
filled  with  dilute  sulphuric  acid  (15°/0)  and  mounted  underneath.  This 
electrode  works  between  a  U  shaped  piece  of  platinum  foil  similarly  treated 
and  is  consequently  of  service  in  damping  the  instrument. 

The  suspension  wire  is  fastened  at  the  top  to  a  torsion  circle  which 
is  fitted  with  a  vernier;  by  means  of  a  micrometric  adjustment,  the  plane 
of  winding  in  the  moveable  coil  can  be  exactly  adjusted  vertically  to 
that  in  the  fixed  outer  coil. 

The  internal  moveable  coil  is  of  ivory  and  the  thin  oval  true  plane 
mirror  is  fixed  thereto  and  also  a  counterweight  for  same  in  the  form 
of  a  brake;  a  bundle  of  soft  iron  wires  can  be  inserted  into  the  ivory 
coil.  The  external  fixed  coil,  which  is  somewhat  oval  in  section  and 
closely  surrounds  the  inner  flat  coil  is  mounted  on  a  brass  case,  cut  across 
to  eliminate  induction,  with  ebonite  flanges;  it  is  set  up  in  two  halves  and 
the  winding  on  each  is  arranged  for  use  either  separately,  parallel  or 
in  series. 

To  facilitate  fixing  the  outer  coil  winding  in  the  magnetic  meridian, 
the  whole  instrument  can  be  revolved  in  its  tripod  stand. 

Sensitiveness  or  constant,  with  coils  of  120  ohms  total  resistance 
in  series,  and  with  the  iron  wire  bundle  inserted:  1  mm  deflection  on 
scale  1  m  distant  =  0.00007  amp.  approx.  (.'.  J  =  0.00007  X  r«). 

Telephonic  currents  can  be  demonstrated  with  this  instrument. 

Price  M.  370.— 


22 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM-FRANKFORT  o.  M. 


View  of  the  inner  coil 
of  No.  378. 


No.  378. 
Unifilar-Electrodynamometer 

Kohlrausch  type. 
(Alternating -current  Galvanometer.) 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  374 


No.  374. 
Tangent  Galvanometer  for  absolute  measurements, 

Kohlrausch  type. 


No.  374.  Tangent  Gal- 
vanometer for  absolute 
measurements  with  non- 
metallic  magnetometer. 

Kohlrausch  type.  To  elimi- 
nate any  appreciable  local 
magnetic  effects  all  un- 
necessary metal  work  is 
removed.  The  current  pas- 
ses through  an  accurately 
turned  ring  of  electrolytic 
copper.  The  magnetometer 
(see  No.  415  p.  72  &  73)  has 
a  magnet  fastened  to  the 
back  of  the  mirror,  which 
acts  also  as  an  air-damper; 
it  can  be  removed  and  a 
compass  with  pointer  (see 
No.  375)  used  instead. 

Price  M.  295.- 


mGr. 


The  table  on  which  the  Mag- 
netometer is  mounted  is  of  such 
a  size  that,  according  to  Helm- 
holtz  (Gaugain)  it  can  be  placed 
about  ?  out  of  the  winding-plane. 


No.375. 


No.  374  a.  As  above,  but  with  magneto- 
meter No.  415 a  (see  p.  72  &  73)  in  which  the 
mirror  can  be  adjusted  as  regards  the  magnet 
which  swings  in  a  copper  damper.  Price  M.  355. — 

No.  375.  Simple  Compass  with  small  steel  magnet  working  in 
jewelled  cap  on  needle  point,  copper  damper  and  check  stop.  Pointer 
reading  on  plate  glass  scale  either  silvered  or  blackened  and  divided  in 
degrees;  for  use  instead  of  the  magnetometer  on  the  Tangent  Galvano- 
meter No.  374  when  measuring  larger  currents.  Price  M.  60.— 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  9 

^ g^g^i ~  ^ 

r\j—  \j£J 

No.  376a. 
Tangent  Galvanometer  for  technical  use. 

No.  376.  Simple 
Tangent  Galvano- 
meter with  one  turn 
of  very  thick  wire 
mounted  to  rotate 
on  a  massive  stand. 
Needle  galvanometer 
with  scale  divided  on 
cardboard  and  with 
inlaid  mirrors  to  facili- 
tate accurate  reading 
of  the  thin  aluminium 
pointer;  magnet  fitted 
with  copper  damper 
and  check  stop. 
Price  M.  210.— 

Range  from  0.1  to 
25  amp.  An  arrange- 
ment can  be  supplied 
to  increase  the  range 
of  the  instrument  up 
to  100  amp.  without 
using  shunts,  by 

withdrawing  the 
needle  galvanometer 
a  certain  measureable 
distance    from     the 
plane  of  the  ring. 
Extra  M.  40.— 

No.  376  a.  As  above,  but  with  a  second  concentric  ring,  smaller 
in  diameter  and  wound  with  2X300  turns  of  fine  silk  covered  wire,  the 
surface  of  which  can  be  measured.  Price  M.  300.— 

Using  these  windings  in  series  or  in  parallel  small  currents  down,  to 
3  milliamperes  can  be  measured  and  also  potentials  determined  -  using 
suitable  resistances  if  necessary  (see  No.  408  page  43). 


25 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Voltameters. 

No.  385.  Kohlrausch  Water- Volta- 
meter. This  is  for  large  currents  up  to 
30  amperes,  with  thermometer  sealed  into 
the  top  of  the  gas  vessel.  It  is  especially 
useful  when  there  is  no  accurate  chemical 
balance  at  hand  for  weighing  silver  or 
copper  deposits.  Readings  with  this  instru- 
ment occupy  but  little  time  and  it  is  excee- 
dingly simple  and  convenient. 

Price:  without  platinum  electrodes  M35.  — . 

Platinum   electrodes:   by   weight  and  at 
market  price,  from  M.  20.—  to  M.  30.—  . 


Vs  n.  Gr 


No.  385b. 


No.  385a.  Silver- Voltameter,  with  large  rod  or  bowl  shaped  silver 
anode  and  stout  platinum  cup,  for  a  current  of  0.25  ampere.  Price : 

without  platinum  cup - M.  60. — 

Platinum  cup,  by  weight  and  at  market  price,  from  M.  40.—  to  M.  60.— 

No.  385b.  Copper  Voltameter  with  several  convenient  arrangements 
to  facilitate  working;  active  surface  of  electrode  about  200  sq  cm,  for  about 
5  amperes.  Price,  without  platinum  electrode  ....  .  M.  70.— 
Platinum  electrode,  by  weight  and  at  market  price  from 

M.  50.—  to  M.  100.— 


J 


26 


r  rn 

,  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Q, 


III. 

Direct  reading  Ampere-,  Volt-  and 
Wattmeters. 


Direct  reading  instruments  offer  considerable  advantages,  compared 
with  those  in  which  the  readings  are  determined  by  turning  a  deflected 
magnet,  or  coil  carrying  the  current,  back  to  its  zero  position.  Firstly, 
because  greater  accuracy  in  the  readings  can  be  obtained  as  there  is 
only  one  pointer  to  be  read  instead  of  two  as  in  zero  instruments;  secondly, 
because  no  manipulation,  such  as  turning  a  torsion  spring  is  necessary, 
and  readings  can  therefore  be  taken  some  distance  away  from  the  instrument 
and  without  any  loss  of  time;  lastly,  because  direct  reading  instruments 
can  be  used  to  measure  a  varying  or  pulsating  current,  and  will  indicate 
the  exact  current  passing  at  any  moment;  provided  that  they  are  suffi- 
ciently damped;  a  point  which  has  received  special  attention  in  the 
following  instruments. 

Special  care  has  been  taken  in  the  design  of  these  instruments  to 
render  them  portable  and  easy  to  use;  for  these  purposes  they  are 
provided  with  circular  levels  and  fitted  with  a  convenient  safety  stop  to 
the  moving  parts  for  travelling  purposes. 

Each  half  of  the  torsion  springs  used  in  these  instruments  is  wound  in 
opposite  direction,  thereby  eliminating  any  temperature  variations  which 
could  otherwise  affect  the  accuracy  of  the  readings. 


27 


HARTMANN  &  BRAUN,  BOCKENHEIM-FRANKFORT  o.  M. 


Direct  reading  Galvanometer  for  current  and 
potential  (patent). 

This    moveable    coil 

No.  530.  'Wlfi  direct  reading  dead-beat 

Galvanometer,  works  on 
the  same  principle  as 
No.  535  and  therefore  pos- 
sesses similar  advantages 
when  used  for  larger  cur- 
rents. The  magnetic  system 
employed,  forming  an  al- 
most closed  circuit,  and  the 
treatment  of  the  magnets 
on  a  similar  method  to  that 
of  Barus-Strouhal,  ensure 
that  the  readings  are  practi- 
cally constant  and  unaffected 
by  temperature  variations. 
The  scale  is  almost  exactly 
proportional  throughout, 
and,  the  pointer  working 
practically  dead-beat,  ren- 
ders this  galvanometer  ex- 
tremely suitable  for  use  as 
a  standard  or  control  instrument.  It  reads  direct  from  one  to  one  hundred- 
fold or  higher.  Made  in  three  types  (with  3  magnets,  not  6  as  shown). 

No.  530.  Direct  reading  Galvanometer  with  moveable  coil,  to 
read  in  volts  and  amperes;  with  series  and  shunt  plug  resistances  arranged 
in  the  base  of  instrument;  reading  from  0.1  to  15  amp.  and  0.1  to  150 
volts.  A  suitable  switch  contact  which  serves  also  as  commutator  for 
current  and  potential  measurements,  enables  readings  of  either  to  be 
quickly  taken.  Price  M.  325.— 

No.  530a.  As  above;  but  as  amperemeter  only;  with  any 
desired  scale  not  exceeding  15  amperes.  Price  M.  180. — 

No.  530b.  As  above;  but  as  voltmeter  only;  with  any  desired 
scale  not  exceeding  300  volts.  Price  M.  180.— 

Shunt  resistance  )  for  use  between  the  terminals  f  Price  M.  45.— 
Series  resistance/  to  increase  the  range  tenfold  j  „  „  105.— 
Other  shunt  and  series  resistances  can  be  supplied,  if  required. 


28 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Direct  reading  Electrodynamometer  and 
Wattmeter  (patent). 


No.  351-533. 


The  principle  on  which  these 
direct  reading  electrodynamic 
instruments  are  constructed  is 
the  action  of  a  suspended  movea- 
ble  double  solenoid  with  similar 
in-  and  external  poles  NS — SN 
on  a  conaxial,  ringshaped  fixed 
solenoid.      As     compared    with 
other    types    of  electrodynamic 
instruments  it  has  the  advantage 
of  an  approximately  equal  scale 
throughout    its    range,    as    any    /-jj 
movement  of  the  suspended  sole-   \ 
noid  in  regard  to  the  fixed  sole-  y 
noid  does  not  appreciably  alter   jf| 
their  effect.  The  instrument  is  per- 
fectly damped  by  an  aluminium 
disc  connected  to  the  moveable 
solenoids  and  working  beetween 
a  powerful  magnet  placed  in  the 

base  of  the  instrument,  a  thick  iron  plate  above  it  shielding  the  moveable 
coils  from  its  effect.  The  instruments  can  be  used  for  measuring  alternating 
currents,  without  alteration,  if  non-inductive  series  resistances  are  employed. 

Made  in  three  types: 

No.  531.  Electrodynamometer  for  large  currents  with   any  desired 
scale  not  exceeding  25  amperes.  Price  M.  340.— 

No.  532.    Electrodynamometer  for  small  currents  (available  also 
as  voltmeter  up  to  150  volts).  Price  M.  340.— 

No.  533.     Wattmeter;   with   any   desired  scale  not  exceeding  1500 
watts  with  15  amps,  current.  Price  M.  340. — 

Commutator  to  extend  the  scale  lower.  „  „  30.— 

If  arranged  as  reflecting  instrument Extra  „  50. — 

„          „       astatic „  „  75.— 

Shunt  and  series  resistances;  according  to  agreement. 


29 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


IV. 

Copies  of  the  Standards  of  the  Imperial 
German  Physico-Technical-Laboratory. 

In  reference  to  the  following  Standard  copies  of  cells,  resistances  and  compen- 
sation apparatus,  we  beg  to  state  that,  if  desired,  we  supply,  at  own  cost,  the  official 
Certificate  from  the  above  laboratory  for  each  instrument. 

No.  551.  Standard  Clark  cell.  The  mercury  electrode  formed  by 
amalgamated  platinum  foil  is  sealed  in  a  porous  cell  with  the  mercurous 
sulphate  paste,  thus  rendering  the  cell  portable.  A  thermometer  projects 
into  the  cell  with  an  external  scale  for  easy  reading.  The  glass  is  pro- 
tected by  a  metal  casing.  E.M.F.  =  1.438  Volt  (at  15°  C.I.  Price  M.  30.- 


No.  554. 


No.  553. 


No.  552. 


Standard  resistances  from  0.1.  1.  10,  &c.  up  to  100000  ohms, 
wound  with  either  Manganin  or  Constantan,  and  therefore  requiring  no 
correction  for  temperature;  with  nickel  plated  electrodes  for  insertion  in 
mercury  cups.  The  resistance  coils  are  accurately  calibrated  and  silver 
soldered  to  the  electrodes;  they  are  mounted  in  perforated  metal  cases 
and  can  therefore  be  used  in  paraffine  baths  for  measurements  at  con- 
stant temperatures. 


No.  552. 

I 

II 

III 

IV 

V 

VI 

VII 

Ohms 

Strongest  current    aJmissible    \     A 
in   petroleum  bath           j    AmP' 

Price  M. 

0.1 

i 

10 

100 

1000 

10000 

100000 

5 

l 

0.3 

0.1 

0.03 

0.01 

0.003 

50 

45 

45 

45 

45 

70 

100 

No.  553.  Standard  Resistance  of  0.01  ohm  can  also  be  used  as 
branch  resistance  for  accurate  current  measurements  up  to  60  amperes; 
similar  design  to  those  previously  described  but  made  from  thin  strip  in- 
stead of  wire ;  fitted  with  two  terminals  at  the  very  ends  of  the  resistance 
for  potential  measurements Price  M.  60. — 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  554.  Standard  Resistance  of  0.001  ohm,  for  use  as  branch 
resistance  for  currents  up  to  250  amperes.  The  electrodes  are  fitted 
with  conical  plugs  on  which  the  accurately  fitted  cable  connectors  can 
be  mounted;  these  connectors  are  bored  and  prepared  to  be  soldered  to 
the  cables;  a  short  circuiting  bar  is  provided  to  cut  out  the  resistance, 
and  the  terminals  for  the  potential  leads  are  mounted  at  the  ends  of  the 
resistance  which  is  of  sheet  manganin  with  large  cooling  surface  and 
mounted  in  metal  case  filled  with  petroleum.  A  cooling  worm  for  use 
with  a  water  supply  and  arrangement  to  stir  the  bath  enable  the  tem- 
perature to  be  easily  controlled.  Price  M.  220. — 

Standard  Resistance  for  0.0001  ohm.   Price  according  to  agreement. 


la  n.  Gr. 


No.  555.    Petroleum  baths,  for  resistances  Nos.  552  and  553.    The 
vessel    brazed   up    from    sheet    copper,    fitted   with    draw    off   cock    and 
thoroughly  nickelled.    Double  mercury  cups  with  terminals  and  nickelled 
are  provided  to  carry  the  resistance  and  leads. 
Made  for  three  or  four  resistances.  Price  M.  70. —  or  80. — 

Extra  for  a  Turbine  stirrer,  to  drive  by  band.*)  M.  30.— 

In  addition  to  the  standard  resistances  Nos.  552—554  we  can,  if  required,  supply 
separate  accurately  adjusted  resistances  of  any  other  size  to  carry  any  desired  current 
up  to  8000  amperes;  made  in  manganin  or  constantan.  These  are  mounted  in  lead 
lined  wood  boxes  for  use  with  petroleum.  Prices  according  to  size  and  requirements. 


*)  Small  Electromotor  to  work  at  various  low  potentials  for  driving  the  stirring 
arrangements  at  prices from  M.  30.—  to  M.  50.— 


31 


HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


Compensation-Apparatus 

for  exact  current  and  potential  measurements. 
Direct  reading. 

The  various  Compensation  Apparatus  about  to  be  described  are 
modelled  after  the  standards  of  the  German  Imperial  Laboratory  and  are 
designed  for  current  and  potential  measurements  by  comparing  the  unknown 
quantity  with  the  E.  M.  F.  of  a  standard  Clark  cell,  which  is  mounted 
in  the  apparatus  but  can  be  removed  if  required  for  other  use.  The 
system  of  measurement  is  a  zero  method  and  the  apparatus  is  of  the  same 
value  for  all  current  and  potential  measurements  as  the  Wheatstone 
bridge  is  for  all  resistance  work;  it  is  in  fact  next  to  the  latter,  the  most 
important  instrument  in  an  electrical  laboratory.  The  requisite  acces- 
sories are  a  battery  with  suitable  switch  and  a  sensitive  galvanometer. 

The  standard  cell  is  protected  from  a  short  circuit  through  a 
ballast  resistance  of  100000  ohms  and  as  the  effect  of  the  compensation 
is  that  no  current  passes,  no  variation  in  its  E.  M.  F.  can  occur. 

The  circuit  is  branched  from  the  main  on  to  the  switch  contacts  of 
two  decade-rheostats  of  10X100  and  10X1000  ohms  and  a  set  of  plug 
contact  resistance  coils,  and  is  adjustable  to  0.1  ohm  thereby.  The 
greatest  care  is  taken  in  calibrating  and  connecting  these  resistances. 
(For  particulars  as  to  official  Certificate  see  heading  to  this  chapter.) 

On  the  left  hand  side  of  the  apparatus  is  a  commutator  to  substitute 
the  standard  cell  for  the  unknown  E.  M.  F.  and  on  the  right  is  a  current  switch 
with  intermediate  contact  for  the  above  mentioned  ballast  resistance. 

Range  from  0.014—  1400  volts,  and  with  suitable  branch  resistances, 
(such  as  Nos.  552  and  554)  from  0.1  milliampere  to  1000  amperes. 


32 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 

' 


No.   556. 
Large  Compensation  Apparatus. 


ca. 


No.  556.  Large  Compensation  Apparatus,  arranged  as  described 
on  opposite  page,  with  a  main  circuit  of  somewhat  over  111000  ohms 
adjustable  throughout,  the  adjustment  for  temperature  of  the  standard 
cell  is  thus  included  in  the  apparatus  and  the  instrument  is  therefore 
direct  reading.  Price  M.  660.— 


J 


33 


r" 

HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  ... 

_^3 ?2^ 

^"  ~T"~ 

Instructions 

for   using  the  large  Compensation 
Apparatus  No.  556. 


1.  Measurement    of  Potentials  between   14  and  1400   volts:     The   points 
between    which   it    is    desired  to  ascertain   the   difference  of  potential  are  connected  to 
B  -J-  and  B  —  and  the  Galvanometer  to  GG,  with  the  commutator  turned  to  the  right  on 
to  c  +  and  c  — .     The  right  hand  switch  contact  is  placed  on  1 X 1000  and  the  left  hand 
on  4x100  whilst  the  plugs  corresponding  to  53  —  t  are  withdrawn  from  the  long  front  row 
of  resistances  where  t  represents    a    figure    read    off  on    the    thermometer  of  standard 
cell.     The    compensation    circuit    is    now    closed    by   turning   the   switch  from  cc    on  to 
100600  and  the  deflected  galvanometer  approximately  brought  back  to  zero  by  plugging 
in  the  horseshoe  and   smaller  row  of  resistances;    and   for   fine  adjustment  turning  the 
switch  on  to  O  and  altering  the  resistances  until  the  galvanometer   gives  no   deflection 
when  the  circuit    is   alternately  made    or  broken.     The    unknown   potential    E   is  then 
0.001  x  W  volt  where   W  is  the  sum  of  all  plugs  withdrawn  plus  the  resistance  of  the 
circular  rheostat  contacts  10000. 

2.  Measurement  of  Potentials  under  14  volts :   a  battery  having  an  E.  M.  F. 
at    least   ten  times   as  large   as  the   one  it  is  desired  to  measure,  is  connected  to  B  + 
and  B  — ;  the  unknown  E.  M.  F.  to  A  +  and  A  —  and  the  galvanometer  to  GG. 

Two  measurements  are  now  necessary:  the  commutator  is  again  turned  first  to 
the  right,  and  the  remaining  operations  are  carried  out  as  in  1  with  the  exception 
that  all  the  plugs  are  withdrawn  from  the  inner  row  of  resistances  and  only  those 
reinserted  which  correspond  to  those  withdrawn  on  the  outer  row  to  evaluate  t. 

Without  considering  the  resistances  in  circuit  when  the  compensation  is  attained, 
the  commutator  is  then  turned  to  the  left,  and  an  approximate  compensation  obtained 
with  the  switch  on  100000;  firstly  by  altering  the  switch  contacts  on  the  circular  decade 
rheostats,  and  finally  —  with  the  switch  on  O  —  by  shifting  the  plugs  in  the  two  front 
rows  of  resistance  coils,  whatever  resistance  plug  is  removed  in  the  one  row  being 
inserted  in  the  corresponding  coil  in  the  other  so  that  the  total  resistance  in  circuit 
remains  unaltered.  The  unknown  potential  A  is  then  0.001  X  W  volt  where  W  is  the 
sum  of  the  resistances  inserted  between  the  switch  rheostat  contacts. 

3.  Measurements   of  current.    These  are  always  correlated  to  differences  ot 
potential  by  passing  the   unknown  current  through    an  accurate    standard   resistance*) 
of  suitable  size   and  determining  the   potential  difference  "at  its  terminals  as  described 
No.  2  above.    The  result   is  read  off  direct  without  working  out   if  the  resistance  em- 
ployed is  10  Ohms  or  a  +  power  of  10  Ohms. 


Nos.  553  &  554,  p.  30  &  31. 


34 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  557. 

Simple  Compensation  Apparatus  for  exact  current 
and  potential  measurements. 


No.  657.  Simple  Compensation  Apparatus,  arranged  as  described 
on  opposite  page,  but  with  main  circuit  ot  somewhat  over  100000  ohms, 
of  which  90050  ohms  is  not  adjustable;  the  results  obtained,  therefore, 
require  correction  for  temperature.  Price  M.  475. — 

This  simpler  instrument  is  used  similarly  to  No.  556. 

To  measure  high  potentials  the  galvanometer  and  the  unknown  E.  M.  F.  are 
connected  as  above;  the  commutator  on  c  +  and  c  —  and  compensation  attained  by 
turning  the  switch  contacts  and  varying  the  plug  resistances.  If  W  represents  the 
resistances  in  circuit  between  the  switch  contact  resistances,  then  the  unknown  E.  M.  F. 

100 
E  =  —  (1453—0  where  t  again  represents  the  temperature  of  the  Clark  cell. 

For  use  with  low  potential  measurements,  the  unknown  E.  M.  F.  is  connected  at 
A  and  a  suitable  battery  (see  opposite  page)  at  B  and  twice  compensated  for;  firstly  the 
Clark  cell  with  the  commutator  on  c  +  and  C  —  and  secondly  the  unknown  E.  M.  F.  with 
the  commutator  on  A.  Then  if  W\  and  W*  represent  in  each  case  the  resistances  in 

circuit  between  the  switch  contacts  A  =  -==-  (1.453  —  0.001  t)  volt. 


35 


r 

^  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  ^ 

~Y- 
v. 

Apparatus  for  measuring  electrical 
resistances. 

No.  389.  Wheatstone-Kirchhoff  Bridge,  Kohlrausch  roller  type.  In  order  to 
obtain  all  the  advantages  of  a  long  branch  circuit  without  the  inconvenient  length, 
otherwise  necessary,  the  wire  in  this  instrument  is  mounted  in  ten  turns  on  a  white 
marble  roller  in  which  the  circumference  is  divided,  on  a  German  silver  ring,  into  100 
parts.  A  small  friction-contact  roller  serves  as  moveable  contact  and  indicates  the  turns 
in  circuit,  and  the  constant  connections  are  formed  through  brush  contacts  of  twenty  wires. 
The  base  of  the  instrument  contains  the  comparative  resistances  of  1,  10,  100,  1000, 
10000  ohms,  —  with  anti-inductive  winding,  Chaperon  system  — ,  which,  through  plugging 
can  be  inserted  on  either  side  of  the  measuring  wire.  Price  M.  250.— 

Cover  for  above  in  wood  with  glass  insets,  to  shield  the  measuring  wire  from 
sudden  changes  of  temperature.  Price  M.  15.  — 

If  desired,  and  at  an  extra  cost,  additional  resistances  can  be  supplied  which  by  ireans  of  plugs  can  be 
connected  to  both  sides  of  the  measuring  wire,  of  the  same  or  4'/g  times  the  resistance  of  the  latter;  or  if  preferred,  with  a 
plug:  arrangement  to  connect  these  resistances  to  either  one  or  the  other  side  of  the  measuring  wire  or  to  make 
them  interchangeable. 

No.  389a.  Wheatstone-Kirchhoff  Bridge  with  stretched  wire  1  metre  long 
and  in  which  the  resistance  can  be  increased  three  fold  by  connecting  similarly  treated 
wires  to  the  two  ends  of  the  measuring  wire.  The  sliding  contact  carriage  is  well 
guided  and  the  frictional  contact  can  be  removed ;  they  work  over  a  scale  accurately 
divided  into  millimetres.  Without  comparative  resistances.  Price  M.  140.— 

A  second'  contact  carriage  and  frictional  contact  for  calibrating  the  measuring 
wire,  or  for  use  of  bridge  as  du  Bois-Reymond  current -compensator,  or  as  Thomson 
(Lord  Kelvin)  double-bridge.  Price  M.  25.— 

Extra  set  of  divisions  for  direct  reading  01  resistance,  referring  to  the  measuring 
wire  only  and  not  to  the  additional  resistances.  Price  M.  10.— 

No.  390.  Induction  apparatus,  Kohlrausch  type,  for  generating  alternating 
currents.  It  is  the  simplest  way,  when  measuring  the  resistances  of  electrolytes,  to 
eliminate  polarisation  by  using  alternating  currents.  This  induction  coil,  which  requires 
3  Daniell  cells  to  work  it,  is  designed  for  this  purpose.  It  has  massive  iron  core  and 
mercury  contact  breaker,  whilst  the  secondary  circuit  is  wound  in  two  parts  which  can, 
by  means  of  plugs,  be  coupled  together  in  any  desired  manner.  Price  M.  140.— 

No.  391.  Universal  Bridge.  Kohlrausch  type,  a  very  simplified  design  of 
instruments  Nos.  389  and  390  (see  page  60).  Price  M.  130.— 

No.  392.  Vessels  with  platinum  electrodes,  Kohlrausch  type;  for  deter- 
mining the  resistance  of  electrolytes.  Two  vessels  connected  by  U  tube  answer  this 
purpose;  the  platinised  platinum  electrodes  have  an  area  of  about  10  sq.  cm.  A  set  of 
three  of  these  compound  vessels  with  connecting  tubes  of  different  diameters  mounted 
on  wire  stands  and  with  one  pair  of  platinum  electrodes,  interchangeable  throughout  the 
set;  the  price  varying  according  to  the  weight  and  market  value  of  the  platinum  from 

M.  70.—  to  M.  80.- 

No.  392a.  As  above,  Arrhenius  type,  in  which  the  glass  vessel  is  cylindrical 
and  mounted  on  glass  base,  the  two  platinum  electrodes  are  superposed  and  the  distance 
between  them  can  be  varied  as  required.  Price  M.  40.—  to  M.  50.— 

Telephones  specially  constructed  for  measuring  see  pageSO.  Price  M.  15.—  &M.  20.— 

J 

36 


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87 


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_  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


o. 


Standard  Resistances. 


All  our  resistance  boxes  with  plug  contacts  are  made  with  the 
greatest  care  and  only  the  best  materials  are  used  and  they  are  always 
repeatedly  calibrated.  The  wire  employed  is  an  alloy  with  a  practically 
negligeable  temperature  coefficient  and  only  used  some  considerable  time 
after  it  is  coiled.  The  coils  are  double*)  wound  and  to  obviate  any  faults 
which  might  occur  from  the  hygroscopic  nature  of  the  silk  covering,  each 
coil  is  kept  for  a  long  time  in  a  hot  air  bath  and  then,  when  all  damp  is 
certainly  removed,  varnished,  or  else  soaked  hot  in  melted  paraffin  which 
penetrates  right  through  the  coil. 

The  inner  and  outer  wires  of  two  neighbouring  coils  are  not  con- 
nected to  one  common  lead  but  are  each  fitted  to  their  own  lead  which 
then  terminates  separately  in  the  metal  block  which  may  be  considered 
as  without  resistance.  It  is  consequently  evident  that  the  sum  of  each  se- 
parately measured  resistance  equals  the  total  combined  resistance. 

Each  metal  block  is  immoveably  mounted  on  the  polished  ebonite 
plate  by  screws  and  pins  and  has  a  conical  hole  in  the  side  to  which  a 
terminal  headed  plug  is  fitted,  any  one  of  the  resistances  therefore  can 
be  used  whilst  obviating  the  joint  resistance  of  the  contact  plugs. 

These  latter  are  made  very  heavy  to  reduce  their  resistance  in  cir- 
cuit and  are  sharply  coned  to  prevent  their  setting  fast  under  variations 
of  temperature,  their  ebonite  tops  are  of  convenient  shape,  solidly  moulded 
on  and  absolutely  immoveable,  care  being  taken,  that  thermo-currents  from 
handling  will  not  occur.  The  cases  are  made  with  large  holes,  which 
can  be  closed  if  required,  to  enable  the  in-  and  external  temperature  to 
compensate  rapidly  and  for  the  purpose  of  introducing  a  thermometer. 
The  coils  are  calibrated  to  a  fractional  part  of  one  onethousandth,  and 
the  official  Certificate  from  the  Imperial  German  Laboratory  will  be 
supplied,  if  desired  for  any  of  these  standards,  at  cost  price. 


*)  The  higher  resistances  will  willingly  be  supplied,  wound  on  Chaperon's  in- 
ductionless  system,  through  which  the  electrostatic  capacity  of  the  resistances  is  con- 
siderably decreased  and  the  resistances  better  adapted  for  telephonic  measurements. 
In  this  case  the  prices  will  be  slightly  increased. 


38 


HARTMANN  &  BRAUN,  BOCKENHEIM-FRANKFORT  o.  M. 


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HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


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HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Standard  Resistance  Boxes: Series  arrangements. 

The  consecutive  arrangement*)  of  resistances  adopted  in  these  series 
rheostats  of  1,  1,  2,  3,  4,  10,  20,  30  et  seq.  enables  each  resistance  to  be 
accurately  calibrated  and  checked  by  the  comparison  of  a  higher  with 
the  combined  sum  of  two  smaller  resistances,  for  which  purposes  the 
jack  plugs  which  are  supplied  with  the  box  will  be  found  very  useful. 
The  additional  resistance  of  Vio  of  the  smallest  resistance  in  the  series 
Rheostat  is  intended  for  interpolation  purposes.  All  the  resistances  are 
marked  on  both  sides  of  the  blocks  and  can  therefore  be  easily  read 
from  either  side. 

Standard  Resistance  Boxes  with  6  plugs  reading  up  to. 


No.  393, 

I 

II  i 

III 

IV 

V 

VI             VII 

Total 

combined  resistance 

1.11 

ll.lj 

111 

1110  1  11100  |111000|  1.11  megohm 

Price  M. 

90 

80 

80 

90 

120 

200 

450 

Series   Rheostats   commencing   with    resistances   of  0.01,   0.1,    0.1, 
0.2,  0.3,  0.4,  1,  2,  3  et  seq. 


No. 

394 

396 

398 

400 

402 

Number  of  plugs  

14 

16 

18 

20 

22 

Highest  single  resistance     p  | 

40 

200 

400 

2000 

4000 

Total  combined  resistance  "o  1 

111.11 

411.11 

1111.11 

4011.11 

11111.11 

Price  M. 

160 

180 

210 

240 

270 

Series  Rheostats  commencing  with  0.1,  1,  2,  3,  4,  10  et  seq. 


No. 

394a 

396a 

398a 

400a 

402a 

Number  of  plugs     .... 

10 

12 

14 

16 

18 

Highest  single  resistance     g 

40 

200 

400 

2000 

4000 

Total  combined  resistance  "o 

111.1 

411.1 

1111.1 

4111.1 

11111.1 

Price  M. 

130 

150 

180 

210 

240 

As  those  figured  in  small  type  are  seldom  asked  for,  they  are  not  kept  in  stock,  and  will  therefore  require  a  longer 
time  for  delivery. 


*)  Any  other  combination  can  be  supplied,  and  the  resistances  adjusted  in  Siemens 
units  instead  of  ohms,  if  desired. 


41 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Standard  Resistance  Boxes 

with  decades  of  equal  or  varying  resistances. 

Branch  Resistance  Boxes. 


in&r. 


No.  403c.  No.  393.  No.  403a. 

Decade  Rheostats  of  10  equal  resistances,  the  circuit  being  made  by  a  single 
plug;  a  second  plug  is  employed  to  vary  the  resistance,  the  circuit  remaining  unbroken, 
and  thereby  eliminating  errors  due  to  variations  ol  resistance  in  the  numerous  plug 
contacts  of  the  Series  arrangement. 

No.  393a  ||      I       |     II     |    III    |      IV      |       V       |       VI      |        VII 


Single  resistances  .   ohms  1  10x0.1 

10X1 

10X1010X100 

10x1000 

lOxlOOCO 

10X100000 

Price  M.        160 

150 

150    1     160 

180 

2250 

500 

Decade  Rheostats  with  resistance  values  of  2x1  and  4x2,  thus  enabling  all 
values  from  1  —  10  to  be  combined  by  the  use  of  two  plugs;  they  are  consequently  more 
convenient. 


No.  393  b              I!       I       |     II 

III 

IV 

V 

VI 

VII 

Total  Resistance  .    ohms  |       1 

10 

100 

1000 

10000 

i  ooboo 

1  megohm 

Price  M.  |     130 

120 

120 

130 

150 

210 

460 

Branch  Rheostats  for  use  with  bridges.  The  two  arms  of  these  rheostats 
are  connected  by  a  plug;  by  means  of  the  two  additional  branch  plugs  they  can  be  used 
independantly  as  branches. 

No.  403.    Branch-Rheostat  with  pairs  of  1, 10, 100  ohms     Price  M.  110.— 

„    403a.  „  „        „       „  10,100,1000  „  „       „   115.— 

„    403b.  „  „        „       „  1,10,100,1000  „  „       „   130.— 

„    403c.  „  „        „       „  1,10,100,1000,10000    „  „       „   200.— 


J 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Shunt  and  Additional  Rheostats  for  use  with  galvanometers. 


No.  404b.  No.  408a.  No.  404. 

Shunt  Rheostats  to  reduce  the  sensitiveness  of  galvanometers,  wound 
with  copper  wire  resistances  and  inductionless  winding;  with  resistances 
J/9,  1/99,  1/999,  and  1/9999  of  the  resistance  of  the  instrument  for  which 
they  are  intended;  assuming  that  the  smallest  resistance  of  the  shunt  is 
not  much  below  0.1  ohm.  With  a  short  circuiting  plug. 
No.  404.  Shunt  Rheostat  with  2  resistances  (  */9  and  Vgg)  Price  M.  120.— 
„  404a.  n  „  „  3  a  (ditto  +  VM»)  „  „  135.— 

„    404b.      „  „  „     4  „          (ditto  4-  V9999)       „       „   160.— 

Additional  Rheostats  with  from  2 — 4  resistances,  wound  with  Con- 
stantan,  of  9,  99,  999,  9999  times  the  resistance  of  the  instrument  for  which 
they  are  intended  and  of  which  it  is  desired  to  extend  the  range;  assuming 
that  the  highest  resistance  does  not  exceed  100000  ohms.  With  a  short 
circuiting  plug. 

No.  408.  Additional  Rheostat  with  2  resistances  (    9  and  99)  Price  M.  120.— 
„    408  a.        „  „  „     3          „          (ditto -f-  999)     „      n  140.— 

n    408b-         »  »  „     4          „          (ditto+9999)      „      „  210.— 

Standard  Rheostat  for  large  currents. 

393 c  I.  Rheostat  with  10  resistances,  each  0.1  ohm,  in  Constantan, 
with  large  copper  and  heavy  nickelled  terminals  for  use  with  mercury 
contacts;  suitable  bow  and  comb  shaped  connectors  are  supplied  to 
couple  the  resistances  either  in  series  or  parallel;  in  the  latter  case  a 
current  strength  of  100  amperes  is  admissible.  The  box  can  be  used  as 
a  petroleum  bath.  Price  M.  500. — 


-13 


r 


HARTMANN  &  BRAUN,  BOCKENHETM- FRANKFORT  o.  M. 


Resistances  for  ordinary  testing, 

with  plug  contacts. 


No.  393d.  No.  398d. 

Resistances,  in  which  the  accuracy  01  calibration  has  not  been  carried 
so  far  as  in  those  previously  described,  are  for  a  great  many  purposes 
however,  sufficiently  accurate,  and  we  therefore  keep  a  stock  of  both  single 
resistances  and  sets  of  four  mounted  on  ebonite;  two,  three,  or  four, 
of  these  sets  can  be  mounted  together  in  one  box,  and  each  set  can  be 
connected  together  by  loose  contact  strips.  The  various  resistances  are 
introduced  into  the  circuit  by  withdrawing  the  respective  plugs,  and  each 
metal  block  is  bored  out  to  take  a  screw  clamp,  so  that  any  shunt  circuit 
can  be  arranged  as  previously  described  on  page  38.  These  resistances 
are  calibrated  to  within  Va  per  cent. 

Single  resistances  as  above  in  wood  case  with  short-circuiting  plug. 


No.  409  d. 

II 

II 

III 

IV           V           VI 

VII 

Ohm.     .     .     . 

0.1 

1 

10           100         1000 

10000 

100000 

Price.     .      M. 

20 

18 

18           18           20 

30 

50 

Rheostats  as  above,  series  arrangement 

No.  393d  II  with  resistances  of     1,       2,       3,       4=         10  ohms,  Pr.  M.  36 

III     „  „          „     10,     20,     30,     40=       100     „          „    „  36 

„     IV     „  „   100,  200,  300,  400=     1000     „  „    „  40 

„      V     „  „  ,,1000,2000,3000,4000=10000     „  „    „  40 

„        „     VI     „  „  „  (10, 20, 30, 40)  X 1000 -100000     „  „    „  70 

Sets  of  the  above  combined  in  one  case 
No.  394d  with  Nos.  393d  II  and  III,       total       110  ohms, 
„     398d     „         „      393d  II,  III  and  IV,     „        1110 
„     402d     „         „      393dII,III,IVandV,  „      11110       „ 

Rheostats   for   branch   circuits,   of  similar  design 
calibrated  more  accurately  than  the  series  rheostats 

No.   403d    I  with  4  resistances     1,     1,     10,     100   ohms,     Price   M.  50 

„         „       II      „       4          „  10,  10,  100,  1000       „  „         „    50 

Bridges  made  from  these  resistances  are  described  on  page  47. 


Price  M.     70 

„       „    100 

„    130 

above    but 


as 


44 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Decade    Rheostats   with  switch  contacts. 

'/4  n.  Gr. 


No.  402a. 

The  Decade  Rheostats  with  switch  contacts  are  each  made  up  of 
10  equal  resistances  of  1,  10,  100,  or  1000  ohms,  calibrated  within 
1/2  per  cent.  As  compared  with  series  rheostats  they  have  the  advantage 
that  the  resistances  can  be  varied  equally  in  parts  of  the  unit  of  resistance 
in  each  decade;  whilst  in  the  series  arrangement  the  variations  can  not 
be  effected  in  this  manner. 


Decade  Rheostats: 
No.  393e    II  with  resistances  10x1 
„        n      HI      „  „  10x10 

„        „      IV      „  „          10x100 

„        „       V      „  „          10x1000 

VI  10x10000 


total        10  ohms,  Price  M.  55.— 

100  „  „       „    55.— 

„      1000  „  „       „    60.- 

10000  „  „       „    60.— 

100000  .    90.— 


Sets  of  above  combined  in  one  case. 

No.  394e  with  decades  393e  II  and  III,    total     110  ohms,  Price  M.  105.— 

„    398e     „           „           „     II,  III  a.  IV,     „      1110      „  „       ,,150.— 

n    402e     „           „           „     II,  III,  IV,  V,    „    11110      „  „      ,,200.- 

Branch  Resistances  with  switch  contacts  each  with  2x3  resistances, 
for  various  arrangements  of  circuit,  accurately  adjusted. 
No.  403 e   I,  with  2  switch  keys,  each  for   1,    10,   100  ohms,   Price  M.  80.— 
„       „       H,     „     2       „          „         „      „   10,100,1000       „  „       „  80.- 

„     III,     „     one  key  for  1,  10,  100  and  the  other  for 

10,  100,  1000  ohms „       „  80.— 

Bridges  made  from  these  decade  rheostats  with  switch  contacts  are 
described  on  page  47. 


45 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Wheatstone  Bridges  with  Standard  resistances, 

with  plug  contacts. 


/4  n.  Gr. 


No.  407. 


These  bridges  are  made  up  with  the  Standard  rheostats  Nos.  398  or  402  (page  41) 
and  the  branch  reostats  Nos.  403  or  403b  combined  with  the  requisite  battery  and  gal- 
vanometer keys.  The  various  parts  are  mounted  together  on  one  piece  of  ebonite  and  are 
so  arranged  that  the  terminals  for  the  unknown  resistance  are  brought  as  close  together 
as  possible.  In  order  to  check  the  resistances  used  in  the  branches,  the  two  arms  can  be 
exchanged  one  against  the  other,  in  which  case  the  long  connector  between  the  series 
and  branch  rheostats  is  removed  and  a  short  one  employed  at  right  angles  to  the  former. 

No.  405.  Standard  Bridge;  with  23  plugs,*)  resistances  of  0.1,  0.1, 
0.2,  0.3,  0.4.  1,  2,  3,  4,  10,  20  &c.  up  to  400,  total  11111  ohms,  besides 
the  pairs  of  1,  10,  100  ohms;  suitable  for  measurement  up  to,  approx. 
110000  ohms.  Price  M.  330.— 

No.  407.  Standard  Bridge;  with  29  plugs*)  resistances  as  above 
but  up  to  4000,  a  total  resistance  therefore  of  111111  ohms,  besides  the 
pairs  of  1,  10,  100,  1000  ohms ;  suitable  for  measurements  up  to,  approx. 
11  million  ohms.  Price  M.  420. — 

If  sufficient  time  for  manufacture  is  accorded,  we  can  supply  bridges 
with  any  desired  combination  of  resistances. 


as  shown. 


'•)   The    plugs    have    ebonite    handles    (as    described    and   illustrated    on    pages 


and   not   capstan  heads 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Bridges  for  ordinary  testing 

with  plug  and  switch  contacts. 


No.  407e. 


No.  405 d.     Ordinary  Bridge  with  plug  contacts,  made  up  with 
the  Series  rheostat  No.  398d  with  3  rows  of  together  1110  ohms  and  the 
branch  rheostats  Nos.  403d  I  or  II  (page  44)  all  mounted  in  one  case  - 
without  keys  —  suitable  for  measurements  up  to,  approx.    100000  ohms. 

Price  M.  150.- 

No.  407  d.  As  above,  but  with  No.  402  d  and  4  rows  of  resistances, 
together  11 110  ohms  and  the  branch  resistances  No.  403d  I  or  II  (page  44) 
suitable  for  measurements  up  to  approx.  1  million  ohms.  Price  M.  180.— 

No.  405  e.  Ordinary  Bridge  with,  switch  contacts:  a  rheostat 
No.  398 e  with  3  decades,  together  1110  ohms,  and  the  branch  resistances 
Nos.  403 e  I,  II,  or  III  (page  45),  and  double-key  contact;  all  mounted 
together  in  one  case,  and  suitable  for  measurements  up  to  100000  or 
1  million  ohms.*)  Price  M.  250.- 

407  e.  As  above,  but  with  rheostat  No.  402  e  with  4  decades, 
together  11110  ohms,  and  the  branch  resistances  Nos.  403  e  I,  II  or  III 
(page  45)  and  double-key  contact,  suitable  for  measurements  up  to  1  or 
10  million  ohms.  Price  M.  300.- 

Simple  Wheatstone  Bridges,  reading  the  resistance  direct  oh 
measuring  wire.  See  pages  60  and  61. 


*)  The  use  ot   a   sufficiently   sensitive   galvanometer   (reflecting  galvanometer)  is 
implied  if  these  high  ranges  are  required. 


rr" 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  c 


No.  506. 

Portable  Universal  resistance-measuring 
apparatus. 


No.  506.  This  Set  of  measuring  instruments  for  use  on  every  range  or  re- 
sistance is  made  up  of  the  series  rheostat  No.  402  combined  resistance  11111.11  ohms, 
the  branch  rheostat  No.  403 b  with  pairs  of  1,  10,  100,  1000  ohms;  the  standard  resistance 
No.  553  of  0.01*);  a  differential  galvanometer  No.  367  with  one  pair  of  coils  of  100  ohms 
and  a  second  pair  of  4000  ohms  and  a  shunt  resistance  No.  404  a  with  3  reduction  re- 
sistances to  suit  the  latter  coils.  A  double  key  and  plug  switch  for  the  various  measuring 
arrangements;  a  battery  commutator  switch  No.  496  to  combine  the  dry  cell  battery 
(10  cells)  in  series,  parallel,  or  separately,  as  required;  and  the  battery  above  mentioned 
in  separate  case.  With  the  exception  of  the  battery,  all  the  above  apparatus  is  mounted 
and  connected  on  an  oak  tray  which  is  fitted  with  strong  handles  for  carrying  purposes, 
and  with  a  lock-down  cover  to  protect  the  various  instruments.  The  combined  appa- 
ratus is  extremely  well  suited  for  accurate  testing  on  widely  extended  systems  of  mains 
from  central  supply  stations  and  is  arranged  for: 

1.  Measuring  resistances  by  means  of  the  Wheatstone  bridge  from  0.1  —  1  million 
ohms. 

2.  Measuring  low  resistances  by  Kirchhoff  s  shunt  method  and  differential  galvano- 
meter; range  from  1  down  to  0.0001  ohm. 

3.  Measuring  high  resistances,  such  as  cable  insulation,  up  to  10  Million  ohms  by 
the  direct  deflection  method. 

The  various  circuit  combinations  for  each  of  these  arrangements  are  fitted  under 
glass  on  the  tray.  Complete  working  instructions  are  supplied  with  each  apparatus. 

Price  M.  1600.- 

If  desired  we  shall  be  pleased  to  modify  this  combination  in  any  way;  especially 
as  regards  the  galvanometer  No.  367  for  which  No.  367a  or  No.  535  can  be  substituted, 
thereby  extending  the  range  for  insulation  testing  in  a  corresponding  degree.  The  dif- 
ference in  value  between  either  of  these  galvanometers  and  No.  367  has  to  be,  in  this 
case,  added  to  the  above  price. 


*)  In  lieu  of  the  second  series  rheostat  shown  on  the  engraving. 


rr~ 


^o  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  641.  Portable  apparatus  to  measure  resistances 
and  potentials. 


No.  641.    Portable   apparatus  to   measure  resistances  and  potentials 

especially  suitable  for  testing  cells.  The  oak  case  contains  a  Wheatstone  bridge  with 
switch  contacts  similarly  arranged  to  No.  407 e  and  a  dead-beat  galvanometer  similar  to 
either  No.  366  or  No.  B36a  and  arranged  to  turn  in  its  seat,  together  with  commutator 
to  reverse  the  battery  poles  and  switch  tor  the  two  different  kinds  of  measurement. 
The  whole  apparatus  is  mounted  ready  for  use  on  the  ebonite  base.  Range,  when  used 
to  measure  resistances,  from  about  0.1  to  1  Million  ohms.  Price  M.  580.— 

Instructions  or  use.  Resistance  measurements.  The  unknown  resistance  is  connected  to  terminals  X, 
the  battery  to  the  terminals  E,  the  switch  U  on  the  contact  E.  Ex  remain  open.  The  switch  contacts  of  tte  comparative 
resistances  a  and  b  are  adjusted  to  a  suitable  proportion,  and  the  decade  resistances  R  are  then  varied  until  the  galvano- 
meter gives  no  deflection  when  the  double-key  is  pressed  down.  Then  x  =  —  R. 

To  measure  potentials  (substitution  method)  a  standard  cell  is  connected  to  E,  the  unknown  potential  to  Ex  and 
the  keys  a  and  b  on  to  the  contacts  Ex.  X  is  left  open.  The  switch  U  is  then  brought  on  contact  E,  and  the  contacts 
of  the  decade  resistances  adjusted  until  the  galvanometer  gives  a  suitable  deflection  when  the  double-key  is  pressed.  U  is  then 
turned  on  to  Ex  and  the  decade  resistances  again  adjusted  until  the  same  deflection  as  before  is  attained.  The  two  potentials 
are  then  in  inverse  proportion  to  the  two  resistances  determined. 


J 


49 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  508. 

Low  resistance  bridge  for  specific  resistance 
measurements. 


No.  508.  This  low  resistance  bridge  is  specially  adapted  for  mea- 
suring the  relative  conductivity  of  various  materials  and  for  testing  arc- 
light  carbons  &c.;  it  is  used  on  the  Wheatstone  bridge  principle,  but  the 
resistances  of  the  contacts  are  eliminated  by  double  readings.  Two  uni- 
versal clamps,  taking  rods  or  wires  of  any  section,  grip  a  certain  definite 
length  of  the  material  (up  to  530  mm)  and  the  reading  is  taken  on  the 
calibrated  wire  and  requires  but  little  calculation.  A  double  key  is  used 
to  close  the  battery  and  galvanometer  circuits  in  succession.  Range  from 
about  0.00001  to  7  ohms.  Price  M.  300.— 

Directions  for  use.  A  straight  piece  of  the  rrut.-rial  to  be  tested  is  inserted  between  the  clamps  K1  and  K2; 
a  sensitive  galvanometer  (such  as  No.  367a,  535,  or  535 1)  is  coupled  between  GG,  and  any  convenient  source  of  current, 
preferably  accumulators,  to  BB.  —  Two  of  the  branch  plugs  for  instance  10:10,  10:100,  10: 1000  according  to  ratio  required, 
are  withdrawn  and  the  sliding  contact  Sj  is  brought  near  Kj  and  S2  adjusted  until  opening  switch  T  does  not  alter  the 
galvanometer  reading;  Sj  is  then  brought  near  Ks  and  Sa  again  adjusted  until  no  deflection  occurs.  The  unknown  re- 
sistance of  the  piece  of  material  included  between  the  two  positions  of  Sj  is  equal  to  the  ratio  of  the  two  branch  resistances 
in  circuit  multiplied  by  the  resistance  of  that  part  of  the  calibrated  wire  included  between  the  two  positions  of  Sz  which  is 
read  off  by  subtracting  the  two  resistances  then  found.  The  length  of  X,  or  in  other  words  the  distance  between  the  two 
positions  of  Sl  is  read  off  exactly  on  the  second  scale  which  is  divided  into  millimetres.  If  it  is  desired  to  measure  other  low 
resistances  such  as,  for  instance,  the  resistance  of  a  coil  of  insulated  wire,  or  the  windings  on  a  dynamo,  the  two  ends  of 
the  unknown  resistance  are  connected  as  before  with  Kt  and  Ka,  using  for  this  purpose  if  necessary,  connecting  wires  of 
suitable  size.  Instead  of  the  sliding  contact  Sj  being  used  a  flexible  wire  is  now  connected  to  b  and  contact  made  thereby 
with  K,  (or  the  end  of  the  unknown  resistance  connected  therewith)  and  the  position  of  the  sliding  contact  Ss  is  then 
determined  and  read  off;  the  flexible  is  then  transferred  to  Ks  and  Sa  again  adjusted  until  the  galvanometer  does  not  deflect 
when  the  circuit  is  repeatedly  made  and  broken. 

The  current  strength  admissible  depends  on  the  section  of  the  material  under  examination.  The  instrument  will 
stand  a  maximum  current  of  about  5  amperes  for  a  short  time,  and  it  is  advisable  to  check  this  by  means  of  an  ammeter 
such  as  No.  380  a  II. 


50 


^  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 
<NT~-  =Y==  —~ 


No.  508a.  Thomson's  (Lord  Kelvin's)  Double  -  Bridge.  By  the 
addition  of  a  second  comparative  rheostat  and  another  moveable  clip  contact 
to  define  accurately  the  length  of  the  piece  of  material  under  examination, 
the  low  resistance  bridge  No.  508  can  be  used  without  further  alteration  as 
a  Thomson's  double-bridge.  It  has  the  same  range  as  No.  508  and  is 
especially  suitable  for  measuring  irregularly  formed  resistances,  such  as 
turns  on  armatures,  &c.  Price  M.  375. — 

K« 


Instructions  for  use.  The  unknown  resistance  is  coupled  to  Ki  and  K2,  and 
a  very  sensitive  galvanometer  to  GG;  the  source  of  current  to  BB.  By  withdrawing 
plugs  in  the  comparative  resistances  any  suitable  ratio  can  be  selected,  the  contacts 
C  and  F  being  adjustable  to  any  desired  position  between  the  various  resistances  for 
this  purpose.  The  moveable  contact  82  is  then  adjusted  along  the  stretched  measuring 
wire,  which  is  graduated  into  thousandths  of  an  ohm,  until  the  successive  contact  key  may 
be  repeatedly  pressed  down  without  causing  a  deflection  of  the  galvanometer.  Then,  taking 

the  ratio  between  the  resistances  —  =  —  as  n,  the  resistance  x  in  circuit  between  Si 

rs        T5 
and  Si  a  —  n-n. 

For  measuring  very  low  resistances  by  Kirchhoff's  differential  shunt-method  the 
following  apparatus  are  necessary.  A  differential  galvanometer  such  as  No.  367  or  367  a 
pages  8  and  9,  No.  535  or  535  a  pages  14  and  15,  or  instead  of  one  of  these  either  No.  371 
or  37 la  pages  10  and  12;  a  standard  branch  resistance  such  as  No.  553  or  554  page  30; 
a  standard  rheostat  with  tenths  of  an  ohm  such  as  No.  398  or  40-2  page  41;  and  a  battery 
key  such  as  No.  492  or  commutator  No.  493  a  page  63. 

The  unknown  resistance  X  is  introduced  into  the 
circuit  in  series  with  the  standard  resistance  R  and  the 
terminals  for  these  two  resistances  are  also  connected 
each  to  one  half  of  the  differential  galvanometer.  The 
rheostat  r  is  coupled  in  whichever  of  these  two  circuits 
is  of  the  lowest  resistance,  and  additional  resistance 
thereby  inserted,  until  the  galvanometer  does  not  deflect 
when  the  circuit  is  made.  The  two  low  resistances  in 
the  main  circuit  are  then  in  the  same  ratio  as  the  two 
larger  resistances  in  the  shunt  circuits. 

It  is  more  convenient  to  use  a  rheostat  in  each  of 
the  galvanometer  circuits,  but  in  this  case  the  second 
rheostat  need  not  be  arranged  with  tenths  of  an  ohm. 
No.  398  a,  page  41,  is  quite  sufficient  for  the  purpose. 


J 


51 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M 


-5-n.Gr. 


No.  614. 
Ohmmeter  to  read  direct  in  Ohms. 

No.  614.  This  Ohmmeter 
reads  direct  in  Ohms  in- 
dependantly  of  the  battery 
strength  employed.  It  con- 
sists of  a  specially  designed 

differential  galvanometer, 
which  is  unaffected  by  the 
earths  magnetism,  though 
without  very  sensitive  astati- 
zation,  and  which  indicates 
by  a  pointer  and  scale  the 
resistance  of  the  circuit  in 
ohms  without  any  further 
calculation.  The  percentage 
ol  error  is  approximately 
the  same  throughout  the 
whole  range  on  the  scale, 
i  and  if  used  with  a  po- 
tential of  50  to  100  volts*), 
for  example,  the  potential 
at  which  an  installation  is 
supplied,  is  about  l°/o.  It  has 

a  range  from  one  to  100  fold  and  by  means  of  a  shunt,  this  range  can 
be  extended  to  1000  fold.  It  is  designed  especially  for  testing  the  insu- 
lation of  an  electric  light  installation  with  a  range  accordingly  from  1000 
to  1  million  ohms.  The  terminals  for  the  unknown  resistance  are  to  the 
left  of  the  instrument  and  battery  terminals  on  the  right;  they  are  cased 
in  ebonite,  and,  together  with  circuit  key  and  automatic  stop  for  travelling 
purposes,  are  mounted  on  polished  ebonite  base,  which  is  enclosed  in 
an  oak  case,  the  lid  being  fitted  with  handle  to  carry  the  instrument. 

Price  M.  250.- 

This  instrument  can  be  supplied  with  any  desired  smaller  range 
and  consequently  more  open  scale;  in  which  case  the  same  degree  of 
accuracy  is  attainable  with  smaller  battery  power. 


*)  60  small  Cells  No.  501  c  (page  66)  in  oak  case  of  same  size  and  shape  as 

for  Ohmmeter Price  M.  120.— 

or  a  Magneto  for  continuous  current  in  a  similar  oak  case.        „       „     50.— 


^g  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  509.    Portable  apparatus  for  measuring  high 

resistances    (Testing  cable   insulation  &c.) 


No.  509.  Portable  apparatus  for  measuring  insulation  resistance  com- 
prising an  accurately  calibrated  dead-beat  galvanometer  of  high  resistance  and  shunt  for 
Vio  sensitiveness,  a  dry  cell  battery  of  approximately  70  volts,  a  key  to  put  the  galvano- 
meter in  circuit  either  with  or  without  shunt,  and  a  two  way  switch  to  put  either  a  com- 
parative resistance  of  100000  ohms  or  else  the  unknown  resistance  in  circuit  with  the 
galvanometer.  This  apparatus  is  all  combined  in  a  very  strong  lock  up  case  for  tra- 
velling purposes,  fitted  with  folding  metal  shod  tripod  legs,  as  shown  in  cut,  and 
weighs  approximately  14  kilogramms.  It  is  especially  suitable  for  use  in  cable  laying. 
Whilst  using  the  method  of  direct  deflection,  the  readings  are  not  affected  by  variations 
of  battery  potential.  Range  from  about  1000  to  15  million  ohms.  Price  M.  375. — 

placed  on  the  contact  marked  VERGL.  (comparative  resistance)  and  the  key  T  pressed  and  moved  on  to  the  contact 
marked.  GALV. ;  a  deflection  is  obtained  of  say  35°.  The  two  way  switch  U  is  then  turned  on  to  the  contact  marked 
UNBEK.  (unknown  resistance)  and  the  key  again  pressed  down,  but  only  moved  on  to  the  contact  marked  GALV.  if  the  gal- 
vanometer needle  is  but  slightly  deflected,  that  is,  if  no  short  circuit  is  present;  a  deflection  is  then  obtained  of  say  8,5°. 
The  values  corresponding  to  these  figures  have  then  to  be  determined  from  the  curve  given  with  each  instrument,  the  readings 
being  ordinates  on  the  curve  whilst  the  values  are  shown  on  the  abscissa  (reciprocal  of  the  resistances)  they  are  120  and 
24.5.  Then  the  unknown  resistance  x  =  12°  X  100  000  _  =  4g979(.  ohmSj  from  which  resu]tj  .„  extreme]y  aC(:urate  work, 

B&O 

the  resistance  of  the  galvanometer  (1000  ohms)  would  have  to  be  subtracted. 

No.  509a.  A  similar  apparatus  as  above  but  arranged  with  Ohmmeter 
No.  614  reading  to  1  megohm,  thus  eliminating  all  further  measurements  or  calculations. 

Price  M.  420.- 


53 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


No.  509b. 

Portable  apparatus  for  measuring  high  resistances 

(large  size). 

No.  609  b.  Portable  apparatus  for  measuring  insulation  resi- 
stances (large  size).  A  weather  proof  case  in  oak,  tongued  and  grooved, 
of  similar  shape  but  larger  than  No.  509  is  so  arranged  that  when  the 
tripod  legs  are  folded  up  it  can,  by  means  of  shoulder  straps,  be  carried 
about  and  erected  where  required  by  one  man.  In  this  case  is  a  larger 
sized  dry  cell  battery  of  over  100  volts  and,  in  lieu  of  the  needle  galvano- 
meter, the  astatic  reflecting  galvanometer  with  telescope  No.  367a  (see 
page  9)  with  the  telescope  bracket  arranged  to  turn  over  for  conveniently 
housing  the  instrument  within  the  case.  A  switch  which  at  the  same 
time  serves  as  a  selector  for  25,  50,  75,  or  100  cells,  a  multiple  contact 
switch  for  the  3  galvanometer  shunts,  and  a  similar  one  for  changing 
the  comparative  resistance  of  100000  ohms  with  the  unknown  resistance, 
and  the  requisite  terminals  for  the  latter,  are  all  mounted  on  a  polished 
ebonite  plate.  This  combination  for  measuring  resistances  by  the  direct 
deflection  method  affords  a  very  high  range  —  maximum  500  megohms  — 
is  also  applicable  to  the  measurement  of  comparatively  low  resistances, 
and  is  therefore  a  very  good  substitute  for  a  travelling  testing-cart  when 
laying  cables.  Price  M.  800.— 

Instructions  for  use:  When  the  mirror  galvanometer  has  been  set  up  and 
adjusted  on  the  open  lid  of  the  apparatus  so  that  the  magnet  swings  freely  and  the  plane 
of  the  coils  lies  approximately  in  the  magnetic  meridian  (operations  which  can  be  per- 
formed by  quite  unskilled  hands)  the  unknown  resistance  is  connected  to  the  terminals 
K  and  Ki  and  the  switch  U  is  turned  on  to  contact  ,,Unbek."  (unknown  resistance),  the 
contact  key  T  which  serves  also  as  battery-selector  being  turned  until  a  suitable  deflection 
is  obtained  when  it  is  depressed.  It  is  advisable,  in  cases  where  even  the  approximate 
resistance  is  unknown,  to  work  with  the  least  sensitive  arrangement  of  the  galvanometer, 
switching  in  by  means  of  Ui  the  smallest  shunt,  as  the  sensitiveness  can  always  be 
increased  by  afterwards  turning  the  switch  Ui  to  the  left  if,  in  its  first  position,  the 
galvanometer  is  not  sufficiently  sensitive  to  give  a  suitable  deflection.  U  is  then  turned 
on  to  ,,Vergl."  thereby  placing  the  comparative  resistance  of  100000  ohms  in  circuit 
in  lieu  of  X,  adjusting  the  sensitiveness  of  the  galvanometer  by  means  of  Ui  until  its 
deflection  is  not  too  different  from  that  previously  obtained,  when  depressing  the 
contact  key  T,  which  of  course  must  be  in  the  same  position  as  in  the  previous  mea- 
surement. These  two  readings  then  give 

_  100000  xcty  s* 

Ox  X  Sv 

ax  and  av  being  the  deflections  obtained  with  the  comparative  and  unknown  resistances 
respectively  and  Sv  and  sx  the  respective  degrees  of  sensitiveness  as  read  off  at  Ui. 


54 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


ca.  V 


No.  509b. 

Portable  apparatus  for  measuring  high  resistances  (large  size). 


55 


r 

HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


,0 


No.  507. 
Cable  testing  cart  and  tent. 


A  well  built  two  wheeled  hand  truck  serves  to  carry  all  the  various 
instruments,  some  of  which  are  removeable  whilst  others  are  mounted 
inside  the  truck  and  are  accessible  on  raising  the  lid  and  dropping  the 
flap  at  back  of  truck.  The  truck  is  fitted  with  an  easily  erected  tent  to 
protect  all  the  instruments  when  in  use,  and  also  with  adjustable  iron 
props  which  enable  it  to  be  firmly  fixed  wherever  required;  provision 
is  also  made  for  carrying  the  light  tripod  stand  on  which  the  mirror 
galvanometer  and  telescope  (No.  367 a)  is  fixed,  to  be  used  under  the  tent 
whenever  measurements  are  being  made.  The  apparatus  contained  in  the 
truck  comprises  a  bridge  with  switch  contacts,  and  an  instrument  for  insu- 
lation measurements  by  the  direct  deflection  method,  all  mounted  with  the 
requisite  keys,  commutators,  battery  selectors  &c.,  but  this  arrangement  can 
be  modified  as  desired.  The  various  instruments  are  mounted  on  a  sliding 
tray,  so  that  if  not  in  use,  they  can  be  pushed  back  from  the  hinged  back  of 
the  cart,  thus  affording  space  for  other  apparatus,  more  especially  a  standard 
voltmeter  and  amperemeter.  A  small  battery  for  use  with  the  bridge 
and  a  larger  one  of  over  100  volts  potential  for  insulation  testing  are 
arranged  in  the  less  accessible  parts  of  the  truck,  and  also  a  magneto 
with  bell  and  galvanometer  for  testing  house  wiring;  a  lock  up  box  is 
also  fitted  in  front  between  the  shafts  to  take  all  requisite  tools. 

Price  (according  to  the  outfit)  from M.  2500.— 


56 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


c 

0) 

-M 

T5 

C 
ctf 


O 


O 

LO 


57 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 

* 


VI.   Apparatus  for  testing  lightning 
conductors  and  earth  connections  for  tele- 
graph and  telephone  stations. 

No.  450.     Nippoldt's  telephone  bridge. 

No.  450.    Nippoldt's  telephone  bridge 

for  testing  the  resistance  to  earth  of  lightning 
conductors.  In  this  instrument  a  bridge  is  com- 
bined with  a  telephone  in  a  clock  shaped  case 
so  that  the  calibrated  wire  is  thereby  protected. 
The  sliding  contact  is  fixed  to  the  graduated 
dial  which  can  be  turned  round  as  required 
and  the  resistance  read  off  direct  in  ohms. 
A  comparative  resistance  and  commutator  are 
also  fitted  in  the  case,  the  latter  is  connected 
to  a  5  cored  flexible  cable  in  which  the  two 
black  and  green  covered  leads  are  connected 
to  the  resistance  to  be  measured,  and  the 
green  to  the  source  of  current,  whilst  the 
brown,  if  necessary,  is  coupled  to  an  earth 
contact.  The  range  is  from  0.1  to  100  ohms; 
resistances  between  100  and  200  ohms  can 
also  be  estimated.  Price  M.  80. — 

The  requisite  current  for  testing  lightning  conductors  and  measuring 
ce  of   electrolytes    is   best    obtained    from    a    small  induction  coil 


nt  for  testing  lightning  conductors  and  measuring 
he  resistance 
with  hi-;h  speed  make  and  break  (high  note)  fed  from  1  or  2  cells. 

Terminals  G    and    Gl   are   provided    on    the   side    of  the   case   if 
galvanometer  is  to  be  connected    for  determining   the  resistance  of  wires  c 
bovc  mentioned  ;   in  this  case  the  short-circuiting   strip  h    is  opened    to    cut   the  telepVior 


No.  451.  Simple  pocket  galvano- 
meter with  index  pointer.  This  in- 
strument is  especially  suitable  for  use 
with  the  lightning  conductor  set 
No.  452  as  its  general  arrangement 
renders  it  extremely  portable;  it  is 
at  the  same  time  useful  for  many 
other  purposes.  A  small  thimble 
magnet  having  sufficient  play  within 
the  copper  damper  to  obviate  the 
necessity  for  levelling  screws  is  sus- 
pended on  a  short  raw  silk  fibre, 
whilst  a  milled  edged  nut  on  the  side 
of  the  case  enables  the  strain  to  be 

taken  off  the  fibre  for  travelling  purposes.  Price  M.  50.— 

Sensitiveness:  1°  deflection  =  0.0001  ampere.  . 


This  instrument  can,  in  combination  with  the  telephone  bridge  above  described,  be  used  for  determining  the  resistance 
of  wires  and  other  solid  materials,  and  especially  in  those  cases  where  induction  occurs,  such  as  coils  and  the  like.  The 
terminals  of  the  two  green  cords  of  the  telephone  bridge  No.  450  are  connected  to  those  marked  P  on  apparatus  No.  452, 
or,  in  the  event  of  this  not  being  available,  to  those  of  a  Leclanche  or  dry  cell,  or  cells  in  series.  In  this  case  the  lever 
on  the  side  of  the  telephone  bridge  is  placed  on  the  mark  I  and  the  brown  cord  is  not  used. 


1 1 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  452. 
Complete  lightning  conductor  testing  set. 


No.  452.  Complete  lightning  conductor  testing  set,  comprising  Nippoldt's 
telephone  bridge  No.  450,  with  induction  coil  for  generating  alternating  currents,  and 
one  to  two  dry  cells  to  work  same,  with  circuit  switch;  fitted  in  walnut  case,  with  drawer 
for  connectors,  galvanometer  (No.  451)  &c.,  with  leather  case  and  shoulder  straps. 
Price,  exclusive  of  galvanometer  and  connectors  M.  120.— 

Directions  for  use.  The  unequal  ends  of  the  black  and  green  flexible  twin  wires  are  connected  to  the  conductor 
the  resistance  of  which  is  to  be  measured,  and  the  ends  of  the  green  flexibles  to  the  terminals  marked  S  on  the  induction  coil. 
The  switch  is  then  moved  on  to  the  contact  marked  TEL.  when  a  humming  sound  will  be  heard  in  the  telephone  which 
either  increases  or  decreases  by  turning  the  dial,  until  the  humming  either  entirely  or  almost  entirely  disappears.  The 
resistance  is  then  read  off  on  the  dial.  The  lever  at  side  must  be  on  I  and  the  brown  flexible  cord  is  not  used. 

If  the  galvanometer  is  to  be  used  to  determine  the  resistance,  the  ends  of  the  green 
flexibles  are  connected  to  the  terminals  marked  P  and  the  switch  is  moved  to  the  contact  marked 
GALV.;  as  for  the  rest  see  page  58. 

Fit'        t          t'  f          dete         '     '     <r     the        e    '<;t  nf     '     '     t  A 

earth  of  lightning  conductors  are  supplied  with  each  set. 

Accessories: 

1.  Folding  earth  plate,  made  up  of  10  tin  sheets  each  25x25  cm 

connected  by  hinges,  and  therefore  extremely  portable,  with  ter- 
minal   Price  M.  15.— 

2.  Earth  contact,  a  steel  drill  with  handle,  a  substitute  for  a  second 

earth  when  testing  lightning  conductors  which  have  only  one  earth. 

Price  M.  6.— 

3.  Connectors  for  coupling   on   to  stranded  lightning  conductors  or 

to  strip  do.  (see  illustration  above)  ....      Price  each  M.  1.75 

4.  Couplings  for  stranded  lightning  conductors     .     .     Price  M.  2.25 

In  certain  cases  the  earth 
above  ground,  and,  to  avoid  cuttin 
a  new  joint,  the  use  of  the  couplii 


lead  of  a  ligthning  conductor  must  be  separated  from  that  part 
the  conductor  which  would  necessitate   making   and  soldering 


illustrated  at  side  is  to  be  recommended. 


5'J 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  391.    Kohlrausch's  universal  bridge. 


No.  391.  Kohlrausch's  universal  bridge  differs  from  most  other 
arrangements  as  the  readings  are  given  on  a  scale  direct  in  ohms  and 
no  reference  to  tables  is  necessary.  The  rheostat  has  comparative  coils 
of  1,  10,  100  and  1000  ohms.*)  When  used  with  a  suitable  galvanometer 
such  as  No.  366,  page  7  or  No.  536 a,  page  15  this  instrument  will  measure, 
with  sufficient  accuracy  for  all  industrial  work,  resistances  of  solid  con- 
ductors (such  as  wires)  from  0.1  to  10000  ohms. 

If,  instead  of  the  galvanometer,  a  suitable  telephone  and  alternating 
current  be  employed,  for  which  purpose  a  small  induction  coil  is  mounted 
with  the  apparatus,  resistances  of  electrolytes,  for  example  the  internal 
resistances  of  cells,  and  the  resistance  to  earth  of  earth  plates  of  lightning 
conductors  can  also  be  determined.  Price  M.  130. — 

Directions  for  use:  Measuring  resistances  of  solid  conductors.  The  unknown  resistance  is  connected 
to  the  terminals  D  and  E;  and  the  battery  (2-3  cells)  to  A  and  B;  the  galvanometer  to  Kj  and  F.  The  plug  S  is  with- 
drawn and  one  of  the  plugs  1,  10,  100,  1000.  The  switch  a  is  moved  on  to  the  contact  marked  GALV.  and  the  pointer  J  is 
adjusted  until  the  galvanometer  does  not  deflect  when  circuit  is  made  and  broken.  The  figure  shown  by  pointer  ]  has  then 
to  be  multiplied  by  the  value  of  the  comparative  resistance  in  circuit,  which  should  always  be  selected  to  bring  the  pointer 
as  near  as  possible  in  the  middle  of  the  scale. 

Measuring  the  resistance  of  electrolytes.  The  battery  for  working  the  induction  coil  is  connected  to 
A  and  C,  and  a  telephone  instead  of  the  galvanometer  to  Ej  and  F,  and'  plug  S  inserted.  The  switch  a  is  moved  on  to 
contact  marked  TEL.  and  the  pointer  adjusted  until  the  telephone  is  silent.  The  resistance  is  read  oft"  and  multiplied  as 
above  described. 

No.  1.     Watch  shape  Telephone  for  determining  the  resistance  of 

electrolytes,  for  use  with  universal  bridge  No.  391,  with  the  fields  specially 

wound  for  the  above  purpose.  Price  M.  15. — 

No.  la.    As  above,  with  ebony  handle.  „       „   20. — 

No.  2  &  2 a.  Telephones,  differentially  wound.  Price  M.  20.—  or  25.— 

*)  If  specially  ordered,  the  Kohlrausch  bridge  No.  391  and  391  a  will  be  supplied  with  rheostats  of  0.1,  1, 
10,  100  ohms  (instead  of  1,  10,  100,  1000)  thus  rendering  them  especially  suitable  for  low  resistance 


HARTMANN  &  BRAUN,  BQCKENHEIM- FRANKFORT  o.  M. 


No.  391a.    Simple  Kohlrausch  bridge. 


No.  391a.  The  simplified  Kohlrausch  bridge  is  the  same  as  the 
Universal  bridge  No.  391  but  without  the  induction  coil,  it  is  therefore 
only  suitable  for  direct  reading  resistance  measurements  of  solid  conductors 
within  a  range  of  0.1  to  10000  ohms,  (if  a  sufficiently  sensitive  galvano- 
meter is  employed).  Price  M.  95.- 


Directions  for  use.    The  ends  of  the  conductor  X  of  which  the 
nals    D    and    E,    the    battery  S    (2-3   cells)   to  A  and  B.     The  galv 


ed  are  coupled  to  the 
F2  and  K1  turning  the  instrument 


resistance  is  to  be  de 

-mil  it  is  in  the  magnetic  meridian,  in  other  words,  until  the  needle  remains  at  zero.  From  the  four  comparative  resistances 
of  1,  10,  100,  1000,*)  that  one  should  be  selected  which  causes  the  pointer  to  remain  as  nearly  as  possible  in  the  middle  ot 
the  scale,  when  the  galvanometer  is  not  deflected  by  making  and  breaking  circuit  with  key  a.  The  reading  of  the  pointer  J 
has  finally  to  be  multiplied  by  the  resistance  in  circuit,  that  is  by  either  1,  10,  100,  or  1000. 

No.  388. 
Portable  set  for  resistance  measurements. 

This  portable  Appa- 
ratus for  resistance 
measurements  com- 
prises the  bridge  No. 
391,  galvanometer  No. 
366,  watch  shape  tele- 
phone No.  1,  three  dry 
cells  No.501a  coupled 
in  series,  all  fitting 
securely  in  separate 

compartments  in  a 
strong  lock  -  up  oak 
case  in  which  a  spare 
compartment  for  con- 
necting wires,  termi- 
nals &c.  is  provided. 
Price  M.  275.- 


Total  weight  approximately  11  Kilo. 


*)  See  foot-note  on  page 


61 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


VII.  Accessories  and  Cells. 


Keys  and  Commutators  for  measuring 
instruments, 

highly  finished  and  mounted  on  polished  mahogany  bases. 

No.  490.    Simple  circuit  closer,   du  Bois-Reymond  type,    with 
sliding  contact  for  large  currents.  Price  M.  10. — 

No.  490a.   Double  successive  key,  of  similar  design.  Price  M.  30.— 


No.  491.         M.  10.-.  No.  491a.         M.  20.—.  No.  491b.       M.  22.-. 

Simple,  double,   and  double  successive  keys,  with  platinum  contacts, 

only  intended  for  small  currents;  the  first  two  types  with  an  arrangement 
for  permanently  closing  the  circuit. 


No.  492  M.  15.—. 


No.  4921).  M.  32.-. 


No.  492a.  M.  28.—. 

Simple,  double,  and  double  successive  keys,  with  detacheable  mercury 

cups  suitable  for  larger  currents;  the  first  two  types  with  an  arrangement 

for  permanently  closing  the  circuit. 


No.  493.     M.  15.—.  No.  493a.         M.  45.—.  No.  493b.       M.  30.—. 

Commutators,  with  plug,  brush,  and  spring  contacts ;  the  first  suitable 
for  small  currents  and  the  two  latter  for  larger  currents. 


82 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  494.         M.  25.-  No.  494a.       M.  30.— 

Revolving  Commutator       and       Rocking  Commutator 

the   former   with   4,    the   latter   with   6   mercury   cup   contacts. 


No.  495.        M.  33.—  No.  495 a.        M.  40.— 

New  Switch  and  Weber  Switch 

the  former  with  4,  the  latter  with  8  removeable  mercury  cups. 


No.  496. 


Battery  Selectors. 

No.  496.    Daurer's  Universal-Pachy- 

trop.  To  enable  a  current  adapted  to  the 
various  classes  of  measurement  to  be  obtained 
from  a  battery  without  inconvenience  or  delay, 
the  use  of  the  above  battery  selector  is  ad- 
visable, by  means  of  which  several  cells  can  be 
connected  either  in  series  or  parallel,  or  any 
single  cell  may  be  selected  as  required.  Made 
with  4,  5,  6,  or  10  pairs  of  terminals.  Price  M.  50.—,  55.—,  60.—,  or  100.— 

Directions  for  use:  Each  cell  or  combination  of  cells  is  connected  to  the  pairs 
of  terminals  fastened  to  the  German -silver  strips  on  the  top  of  the  apparatus,  care 
being  taken  that  the  poles  of  the  cell  or  cells  are  correctly  coupled  to  the  terminals  as 
marked.  The  current  is  taken  off  from  the  larger  pair  of  terminals.  According  to  the 
position  of  the  levers  the  following  combinations  are  then  at  once  available: 

1.  All  cells  cut  out  of  circuit:  every  lever  in  its  mid-position. 

2.  All  cells  coupled   in   series:   the  two  outermost  levers  pushed   down   and 
all  the  others  pushed  up. 

3.  All  cells  coupled  in  parallel:  all  the  levers  pushed  down. 

4.  Any  single   cell:   the  two   levers  corresponding  thereto   pushed  down,   and 
all  the  rest  in  their  mid-position. 

5.  2  or  more  cells  coupled  in  series:  the  two  levers  between  which  the  cells 
to  be  connected  are  mounted  are  pushed  down,  and  the  lever  or  levers  between 
these  are  pushed  up,  the  remaining  levers  in  their  mid-position. 

G.  2  or  more  cells  coupled  in  parallel:  the  corresponding  levers  commencing 
from  the  right  hand  are  pushed  down,  the  remaining  levers  in  their  mid-position. 

Battery-selectors  with  plug  contacts  in  various  designs  specially 
quoted  for  on  receipt  of  particulars  of  requirements. 


68 


"^  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Keys  and  Commutators 
for  capacity  and  insulation  measurements. 


No.  499a. 


No.  497a. 


No.  498. 


No.  497. 


No.  499. 


We  have,  in  designing  these  various  keys  and  commutators, 
specially  borne  in  mind  the  necessity  for  obtaining  as  high  a  degree  of 
insulation  as  possible  between  all  parts  carrying  current,  and  to  earth; 
for  this  purpose  not  only  the  spring  contact  strips  but  also  the  various 
terminals  are  all  mounted  on  sufficiently  high  ebonite  pillars  which  are 
so  arranged  and  designed  as  to  facilitate  access  thereto  from  all  sides  to 
enable  all  dust  and  moisture  to  be  removed. 

No.  497.  Charge  and  discharge  key  for  capacity  measurements  in 
condensers  or  cables,  on  Sabine's  principle.  Price  M.  30.— 

The  spring  contact  which  is  to  be  connected  to  the  cable  or  terminal  of  condenser 
is  kept  free  when  the  lever  is  in  its  backward  position;  if  this  is  in  its  mid  position  the 
spring  contact  touches  the  contact  which  is  to  be  connected  to  one  pole  of  the  battery 
(Charge  position);  if  the  lever  is  in  its  forward  position,  contact  is  made  with  the  lower 
fixed  contact  which  is  to  be  connected  to  the  galvanometer  (Discharge  position).  The 
fourth  terminal  is  for  earth,  galvanometer,  the  second  terminal  of  condenser  and  the 
other  pole  of  battery. 


64 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  497  a.  Cable  key  for  insulation  measurements  for  reversing 
battery  poles.  Price  M.  55.— 

Two  spring  contacts,  one  of  which  is  connected  to  earth  and  the  other  to  the 
galvanometer,  are  pressed  separately  and  alternately  against  an  upper  contact  connected 
to  the  —pole  of  battery  and  a  lower  contact  connected  to  the  +pole  of  same:  in  the 
latter  case  the  ebonite  lever  is  in  its  forward  position,  in  the  former,  in  its  mid  po- 
sition, if  the  lever  is  in  its  backward  position  the  spring  contact  remains  free  between 
the  others. 

This  key  is  even  more  convenient  than  that  previously  described  for  capacity 
measurements,  the  method  of  connection  and  manipulation  remaining  as  before.  For  this 
purpose  the  free  terminal  is  again  connected  to  earth,  galvanometer,  condenser  and  battery, 
the  cable  to  one  spring  contact  and  the  remaining  terminal  of  condenser  to  the  other. 

No.  498.  Compensation-key  for  capacity  measurements  by  Thomson's 
(Lord  Kelvin's)  method.  Price  M.  90.— 

One  terminal  of  each  of  the  two  condensers  which  are  to  be  compared  is  con- 
nected to  each  of  the  two  outside  spring  contacts,  one  ot  the  galvanometer  leads  is  taken 
to  the  centre  spring  contact  whilst  the  other  together  with  the  remaining  condenser 
terminals  are  coupled  to  the  earth  terminal.  Charge  and  discharge  are  effected  by  means 
of  the  lever  at  side,  in  its  mid  position  all  three  springs  are  free  from  .contacts,  when 
turned  backwards  the  outer  springs  make  contact  with  the  battery  contacts  for  charging; 
when  turned  forwards  the  outer  springs  first  make  contact  with  a  metal  bridge,  thus  the 
condensers  discharge  against  each  other;  on  further  turning,  the  centre  spring  contact 
also  comes  against  the  bridging  piece  and  any  residual  charge  is  thereby  discharged 
through  the  galvanometer  to  earth. 

The  series  rheostats,  page  41,  having  branch  plugs  at  side,  are  especially  suitable 
for  use  as  variable  resistances  through  which  the  battery  is  placed  in  circuit. 

No.  499.  Spring  commutator  for  insulation  measurements,  with 
four  fixed  terminals  which  can  be  coupled  in  pairs  or  alternately  through 
two  spring  contacts  mounted  on  an  ebonite  handle  to  turn  as  required, 
similar  in  principle  to  the  revolving  commutator  No.  494.  Price  M.  40. — 

No.  499a.  Switch  with  six  mercury  cup  contacts,  mounted  on  ebo- 
nite pillars,  resembling  the  rocking-commutator  No.  494a.  Price  M.  55. — 

Complete  sets  of  apparatus  for  insulation  and  capacity  measurements, 
mounted  on  marble  bases,  with  all  connections  ready  for  use  can  be  sup- 
plied; the  price  depending  on  the  apparatus  required. 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Dry  cells  for  measuring  purposes. 


n.  Gr. 


These  dry  cells  are  especially  suitable  for  measuring  purposes  on 
account  of  their  high  electromotive  force,  but,  like  other  dry  cells,  they 
are  not  designed  to  give  large  currents,  and  it  is  therefore  adviseable  to 
protect  them  from  short  circuit  or  discharge  by  a  very  small  resistance; 
the  internal  resistance  and  electromotive  force  in  these  as  in  other  dry 
cells  is  not  absolutely  constant,  but  when  the  cells  are  exhausted  they 
can  be  repeatedly  recharged;  they  are  supplied  in  the  two  following  types. 

No.  501  a  in  strong  zinc  case,  rectangular  8x4x12  cm,  15.5  cm 
high  including  terminal;  weight  1  Kilo.  Price  each  M.  2.75 

No.  501  c  in  insulating  case,  square  section  3x3x7  cm,  9  cm  high 
including  terminal;  weight  120  grammes.  Price  each  M.  1.50 

Directions  for  recharging:  The  corresponding  poles  of  the  cell  to  be 
recharged  and  the  source  of  current  are  connected  together;  and  to  obtain  the  best 
results,  the  cells  should  be  regenerated  as  soon  as  the  E.  M.  F.  falls  below  1  volt, 
without  waiting  until  they  are  almost  entirely  run  down.  No.  501  a  should  be  charged 
at  about  0.4  amperes  and  No.  501  c  at  about  0.2  amperes  for  a  few  hours. 


GG 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Portable  batteries  in  wood  cases. 


Portable  batteries,  in  strong  oak  cases  for  measuring  purposes. 
Cells  of  No.  501  a  type,  not  exceeding  30  in  number,  and  qf  No.  501  c  not 
exceeding  100,  are  securely  mounted  for  travelling  purposes  in  case, 
fitted  if  desired  with  commutator,  selector,  &c.  Where  space  is  available 
the  larger  size  cells  are  preferable,  as  these,  with  a  low  internal  resis- 
tance, vary  but  slightly  in  voltage  in  the  course  of  time.  The  smaller 
cells  are  especially  suitable  for  use  with  portable  apparatus  for  determining 
insulation,  as  in  this  case  it  is  not  so  much  a  question  of  the  internal 
resistance  of  the  battery  as  of  obtaining  the  highest  possible  potential 
within  the  smallest  space. 

No.  502.  Battery  of  30  cells  No.  501  a,  coupled  in  series,  in  oak 
case,  with  compartments,  and  selector  for  10,  20,  or  the  total  number 
of  cells.  Price  M.  150.- 

Other  combinations  quoted  for  on  receipt  of  particulars. 


67 


r 

HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


VIII. 

Instruments 
for  magnetic  measurements. 


No.  410.  Portable  Bifilar- Variometer  for  terrestrial  mag- 
netism; Kohlrausch  type.  This  type  differs  from 
the  Gauss  pattern  by  the  use  of  a  small  tubular 
magnet  which  consequently  causes  but  slight  mag- 
netic disturbances  in  its  immediate  neighbourhood. 
The  bifilar  suspension  consists  of  two  extremely  fine 
brass  wires  (0.05  mm  dia.)  30  cm  long  and  about 
8  mm  apart.  The  magnet  is  powerfully  damped, 
and  to  ensure  its  permanency  it  is  several  times 
exposed  to  a  high  temperature  and  for  long  periods 
in  accordance  with  the  Barus  Strouhal  method.  The 
variometer  is  easily  mounted  and  its  constants  de- 
termined by  the  torsion  head  which  is  fitted  with 
vernier  and  micrometer  screws.  To  control  the  in- 
variability of  the  suspension  an  adjustable  mirror  is 
mounted  on  the  torsion  tube.  Magnet,  and  mirror, 
capable  of  being  turned,  are  carefully  shielded  from 
air  currents,  and  a  thermometer  is  mounted  in  the 
damper .  .  .  M.  350. 

(Wiedemann's  Annalen  XV,  1882,  page  553.) 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  410. 
Portable  B  if  ilar-  Magneto  meter 

Kohlrausch  type. 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Ji3  ^ 

2.  o 

o  " 

3  £ 


70 


HARTMANN  &  BRAUN,  BOCKENHEIM -FRANKFORT  o.  M. 


No.  411.  Intensity- Variometer  for  terrestrial  magnetism  with  four 
controlling  magnets:  Kohlrausch  type.  The  needle  in  this  instrument 
is  formed  of  a  true  plane  steel  mirror  and  controlled  by  four  small  bar 
magnets  which  give  a  very  constant  magnetic  field  in  their  immediate 
neigbourhood.  It  is  deflected  90°  from  the  meridian  so  that  declination 
variations  have  no  effect.  As  compared  with  the  instrument  previously 
described  this  offers  the  advantage  that  the  sensitiveness  can  be  adjusted 
to  any  desired  amount,  and  its  constants  are  easily  determined  by  means 
of  the  graduated  circle  above  which  the  framework  supporting  the  magnets 
revolves.  A  small  reading  telescope  with  opal  glass  scale  is  mounted 
direct  on  the  instrument.  This  apparatus,  which  is  very  portable,  can 
also  be  used  as  local  variometer  to  determine  the  variations  of  horizontal 
magnetic  intensity  between  different  places  with  extreme  accuracy  (1:10000) 

Price  M.  375.- 

(Wiedemann's  Annalen  XV,  1882,  page  540.) 


ca.  */4  n.  Gr. 


No.  411a. 
Simple  Local-variometer,  Kohlrausch  type. 

No.  411a.     Simple  Local-variometer  to  determine  local  variations 
in  the  horizontal  intensity.    Whilst  the  method  of  using  and  the   general 
design   of  this   instrument  remain   the  same  as  in   the    above    described 
variometer  No.  411;    in   this   instance   every  thing  is  simplified   and  the 
entire  instrument  rendered  more  portable.    The  combination  of  4  magnets 
is  replaced  by  one  magnet  of  a  suitable  form,   which,   together  with  the 
graduated   circle   is    adjustable    concentrically  below    the    magnet  needle 
which    is    here   supported   on   a  pivot.     Suitable  clamping  screws  ensure 
the  constancy  of  the  turning-angle,  and  the  instrument  is  sufficiently  ac- 
curate for  most  purposes  (1  :  1000)  ........     Price  M.  200.— 

(Wiedemann's  Annalen  XXIX,  1886  page  47.) 


7L 


^  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 

' 


No.  412.  Absolute  Bifilar- Magnetometer,  Kohlrausch  type.  In 
contrast  to  other  magnetometers,  the  method  of  suspension  here,  is  by 
two  very  fine  wires  widely  separated  from  each  other  (12  cm).  On 
account  of  the  accuracy  with  which  these  conditions  can  be  determined, 
the  deflections,  when  the  magnet  is  reversed,  give  the  product  of  the 
bar  magnetism  and  the  terrestrial  magnetism  in  absolute  measure. 
Simultaneous  observations  of  a  unifilar  magnetometer  (see  No.  415  and 
415  a)  deflected  by  the  magnet  give  the  earth's  magnetic  force  in  absolute 
measure.  This  method  is  preferable  because  no  time  observations  are 
required  and  neither  temperature  nor  locally  induced  magnetism  can 
affect  the  result. 

The  apparatus  comprises  the  suspension  with  divided  circle,  tubular 
magnet  with  rotatable  mirror,  damper  for  use  with  fluids,  and  vibration 
chamber.  Price  M.  230.— 

(Wiedemann's  Annalen  XVII,  1882,  page  737.) 

No.  413.  Absolute  Bifllar- Galvanometer,  Kohlrausch  type.  A 
wire  ring  20  cm  diameter  with  a  large  number  of  turns  is  bifilar  suspended 
in  a  similar  manner  to  the  previous  instrument.  Its  deflection  by  means 
of  a  current  gives  the  product  of  the  current  strength,  area  of  coil  and 
terrestrial  magnetism.  In  combination  with  a  tangent  galvanometer  (see 
Nos.  374  to  376)  or  with  a  magnetometer  (see  Nos.  415  and  415a)  it  can 
be  employed  either  for  absolute  measurement  of  the  current  or  of  the 
terrestrial  magnetism. 

Suspension,  wire  ring  with  rotatable  mirror  and  vibration  chamber. 

Price  M.  250.- 
(Wiedemann's  Annalen  XVII,  1882,  page  737.) 

No.  415.  Unifilar  Magnetometer,  Kohlrausch  type,  with  a  small 
magnet  mounted  at  back  of  mirror,  which,  working  in  a  very  narrow 
chamber  with  inserted  vanes,  acts  as  an  efficient  air  damper. 

Price  M.  120.— 

No.  415  a.  Unifilar  Magnetometer,  Kohlrausch  type,  later  pattern, 
with  ring  magnet,  in  copper  damper;  the  mirror  adjustable  against  the 
magnet  and  the  entire  system  shielded  from  external  air  currents  by  a 
wooden  case.  Price  M.  180. — 

No.  420.  Compensation  Magnetometer,  Weber  and  Kohlrausch 
type,  with  stand  and  vibration  chamber.  Price  M.  300.— 

No.  421.  Gauss -Weber  Magnetometer,  for  mirror  readings,  to 
determine  the  horizontal  component  of  the  earth's  magnetic  force,  and 
also  the  declination;  with  magnets  8  cm  long  and  rails  for  same  50  cm 
long,  copper  damper,  vibration  chamber  and  all  other  requisite  accessories. 

Price  M.  400.- 


72 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  c 


<D 


73 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  425. 
Earth  Inductor,  W.  Weber's  type. 


n.  Gr. 


No.  425.  Earth  Inductor,  W.  Weber's  type,  for  measurement  of 
terrestrial  magnetic  inclination,  with  induction  ring  20  cm  diameter,  very 
strongly  built  and  fitted  with  convenient  arrangements  for  adjustment.  The 
mirror  magnetometer  which  is  included  in  the  apparatus  for  the  purpose 
of  adjusting  it  to  the  magnetic  meridian  renders  it  also  available  as  a  tangent 
galvanometer Price  M.  650. — 

No.  425a.    As  above,  with  induction  ring  40  cm  dia.  Price  M.  850. — 

No.  4S7.    Astatic  Reflecting  galvanometer*)  for  use  with  the  earth 
inductors  Nos.  425  and  425  a  with  corresponding  vibration  periodicity  and 
extreme  sensitiveness  and  which,   by  means  of  an  easily  inserted  copper 
damper  and  double  winding  is  available  for  galvanic  work. 
Price  M.  400.- 

*)  See  page  19. 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  ^ 

r^j f^j5* CX"> 

No.  426. 
Differential  Earth  Inductor.     L.  Weber's  type. 


No.  426.  Differential  Earth  Inductor,  L.  Weber's  type,  for  deter- 
mining rapidly  the  angle  of  inclination.  Two  coils,  as  near  as  possible 
duplicates  of  each  other  and  interchangeable  in  their  bearings,  with  their 
axes  at  right  angles  to  each  other  are  revolved  together.  The  measure- 
ment is  made  with  a  differential  galvanometer  and  occupies  scarcely  one 
minute.  The  strength  of  current  is  equalised  in  both  coils  by  inserting 
resistances.  The  tangent  of  the  angle  of  deflection  is  then  equal  to  the 
ratio  of  the  resistances  of  both  circuits.  Price  M.  2200.— 

(Sitzungs-Berichte  der  Akademie  der  Wissenschaften,  Berlin,  XLIX,  December  1885.) 


75 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  431. 
Large      .^    Electromagnet. 


No.  431.  Large  Electromagnet,  made  from  Swedish  charcoal  iron, 
with  vertical  limbs  40  cm  high  and  70  mm  in  diameter,  pole  pieces  of 
square-section,  with  hole  bored  through;  they  can  be  adjusted  and  clamped 
in  any  desired  position  on  the  surfaces  of  the  limbs.  The  winding,  of  3  mm 
copper  wire,  is  in  four  removable  sections  on  brass  forms  and  each 
form  has  suitable  terminals  mounted  thereon  to  enable  the  windings  to 
be  easily  connected  in  series  or  parallel  as  required.  The  stand  is  fitted 
with  rollers  for  convenience  in  moving  the  instrument,  and  screws  are 
provided  to  fix  it  in  any  desired  position.  A  commutator  and  vertical 
pillar  with  a  small  adjustable  table  are  also  mounted  on  the  stand,  and 
a  small  piece  of  bismuth  and  a  glass  trough  for  diamagnetic  experiments 
are  sent  with  the  apparatus.  Three  different  pairs  of  insets  for  the  pole 
pieces  in  various  well  known  forms  are  also  included.  Price  M.  1400. — 

Extra  apparatus: 

Wai  ten  ho  fen  Pendulum  for  experiments  in  induction.     Price  M.  255.— 
Polarisation    Apparatus    for   experiments  in   diamagnetism;    fitting  into 

the  holes  bored  in  pole  pieces Price  M.  110.— 

Parallelepipedon  with  partially  silvered  surfaces,  made  in  Faraday  glass 

(silicate  and  borate  of  lead) Price  M.  30.— 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  504.     Bismuth  Spiral 
for  measurements  of  magnetic  fields, 

Lenard's  type. 


n.  Gr. 


Measurements  of  the  intensity  of  magnetic  fields  by  means  of 
Lenard's  bismuth  spiral  are  effected  through  the  change  of  resistance 
which  occurs  in  bismuth  when  in  a  magnetic  field.  In  this  instrument  a 
thin  wire  of  chemically  pure  bismuth,  well  insulated,  is  double  wound 
as  a  flat  spiral,  and  the  ends  soldered  to  two  flat  copper  strips  which  are 
fitted  with  requisite  terminals  and  mounted  in  an  ebonite  handle;  the 
spiral  is  cemented  between  two  thin  mica  discs  to  protect  it  from  damage. 
As  the  entire  thickness  of  the  spiral  is  only  about  1  mm,  the  instrument 
can  be  used  in  very  confined  spaces,  as  for  instance  in  the  clearance 
space  between  pole  pieces  and  armature  of  a  dynamo.  The  alteration 
in  resistance  affords  the  means  for  determining  the  number  of  lines  of 
force  in  the  field  tested,  1000  representing  approximately  5°/o  alteration 
in  the  resistance;  the  calibration  curve  which  is  supplied  with  each  instru- 
ment gives  the  relative  proportion  with  greater  accuracy.  Price  M.  50. — 


/ 

^ 

' 

/ 

s 

IL 

s* 

/s 

£1 

S 

^ 

KJ 

\S* 

/ 

^S 

S* 

- 

-< 

F-3 

So^t 

tw\A 

4/WX. 

oty 

100ft     2000    3000    4000    5000    60007000     8000     9000   10000   11000  12000  13000  14000  15000  1«OC 
F  =  number  of  lines  of  force. 

Reduced  copy  of  a  calibration  curve  which  enables  the  relation  between  the  increase  in  resistance  of  the  bismuth 
spiral  and  the  number  of  lines  of  force  in  the  field  under  examination  to  be  determined  direct.  The  ordinate  values  represent 
the  increase  in  resistance  Z,  determined  from  the  resistance  of  the  bismuth  spiral  Wo  in  field  zero  and  WF  in  field  F. 


J 


77 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  56O.     Simple  apparatus 
for  investigating  the  magnetic  properties  of  iron 

by  means  of  the  bismuth  spiral. 


No.  560.  This  apparatus  for  investigating  the  magnetic  pro- 
perties of  various  classes  of  iron  consists  of  an  oval,  wire  wound 
electromagnet;  one  side  is  easily  removable  and  the  piece  of  iron  to  be 
tested  can  be  inserted  in  the  space  thus  provided  in  combination  with  a 
bismuth  spiral  No.  504  fixed  in  the  narrow  air  space  then  remaining;  by 
means  of  a  micrometer  attachment  mounted  on  the  apparatus  this  air 
space  can  be  exactly  determined.  The  winding  is  designed  to  give 
comparatively  strong  fields  with  small  currents.  Price  M.  210.— 

Instructions  for  use:  The  iron  to  be  tested  is  adjusted  as  accurately  as  possible  in  size  to  the  standard 
removable  bar  and  the  intensity  of  the  field  is  determined  by  means  of  the  bismuth  spiral  for  both  the  standard  bar  and 
the  bar  under  examination  using  the  same  number  of  ampere  turns  in  each  case.  These  two  results  give  the  comparative 
values  of  both  the  standard  and  the  testbars,  and,  if  the  magnetic  properties  of  the  standard  bar  have  been  plotted  as  a 
curve,  those  of  the  bar  under  examination  can  easily  be  plotted  and  compared  therewith. 

Galvanometer  No.  335  page  14  is  specially  adapted  for  this  instrument  as  it  is 
not  affected  by  other  electromagnets  in  its  proximity. 

The  following  arrangement,  using  a  bridge,  is  very  convenient  for 
determining  the  intensity  of  magnetic  fields. 

Two  resistances,  ot  1  ohm  each,  OD  and  DC, 
-e  connected  to  a  stretched  measuring  wire  fitted 
.  -ith  sliding  contact  Sj  also  a  resistance  E  equal  to  that 
of  the  bismuth  spiral  at  its  lowest  temperature  and 
lastly  a  second  measuring  wire  with  sliding  contact  S2. 
The  spiral  is  connected  to  S,  and  S2,  the  galvanometer 
to  A  and  C,  and  the  battery  to  B  and  D.  The  bridge 
is  then  balanced  with  the  spiral  in  field  zero  by  placing 
the  sliding  contact  S,  on  the  zero  of  the  measuring 
wire  and  adjustin<*  S2  until  balance  is  obtained,  then, 
as  01)  =  DC,  DS,  =  WO,  i.  e.  equal  the  resistance 
of  the  spiral  at  the  prevailing  temperature.  Without 
moving  Sa.  S.  is  then  adjusted  with  the  spiral  in 

•yjf  \L* 

the    field    to   be   determined ;    then  OF 


i.  e.  is  equal  to  the  increase   in  resistance  Z    of  the  spiral.     The  me  „         _ 

and,   provided  the  same  spiral  is  always  employed,  can  also  be  scaled  to  give  the  intensity  of  the  field  d 


We 
wire  can  be   scaled  to  give  this  quotient  di 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  560a. 

Complete  apparatus  for  investigating  the  magnetic 
properties  of  iron. 


No.  560 a.  Complete  apparatus  for  investigating  the  magnetic 
properties  of  iron.  The  apparatus  illustrated  herewith  is  especially 
suitable  for  use  where  it  is  desirable  to  make  the  test  as  quickly  and 
easily  as  possible,  without  having  first  to  connect  for  this  special  purpose 
the  various  instruments  perhaps  existing  for  accurate  resistance  measure- 
ments ;  it  is  extremely  useful  for  factories,  works,  such  as  foundries,  iron 
works  &c.,  where  a  staff  competent  to  carry  out  electrical  testing  is  not 
maintained.  It  comprises  the  electromagnet  No.  560  with  bismuth  spiral,  a 
switch  for  heavy  currents  and  an  ammeter,  unaffected  by  neighbouring 
magnetic  fields,  to  measure  the  current  employed  in  exciting  the  electro- 
magnet, a  galvanometer  and  double  key  for  the  measuring  current,  and 
lastly  a  specially  arranged  bridge  on  which  the  number  of  lines  of  force 
can  be  read  off  direct.  All  the  instruments  are  mounted  on  a  mahogany 
base  board  ready  for  use  and  so  arranged  that,  using  the  instructions 
printed  below,  comparative  tests  of  various  samples  can  be  made  without 
any  previous  training.  Price  M.  585. — 

lion    fc 


Instruction  for  use:  A  test  piece  of  the  iron  to  be  examined,  as  near!) 
standard  (a.  cylinder  200  mrn  long  and  25  mm  diameter),  is  prepared  and,  encircled  by  the  i 
the  poles  of  the  electromagnet  with  iis  left  hand  face  bearing  firmly  ag. 


s   possible   the   sam.-  size  .is  the 
veable  wire  coil,  placed  between 
he    magnet    pole.     An  adjustable  sourci  of 

current,  preferably  accumulators  capable  of  discharging  np  to  a  rate  of  15  amperes,  is  coupled  to  the  large  terminals.  The 
testing  battery  of  2  or  3  cells  is  connected  to  terminals  b.  The  sliding  contact  St  of  the  front  measuring  wire  is  then 
placed  on  the  zero  mark  of  its  scale  and  contact  for  the  measuring  current  made  by  depressing  the  key  t,  adjusting  the 
sliding  contact  Sg  of  the  measuring  wire  at  back  and  repeatedly  making  and  breaking  contact  with  t  until  the  galvano- 
meter ii  not  deflected.  The  exciting  current  is  then  switched  on  by  switch  T,  measured  by  the  ammeter,  and  the  measuring 
battery  again  brought  in  circuit  by  t;  then  leaving  S8  in  its  present  position  on  the  measuring  wire  at  back,  S,  on  the 
front  measuring  wire  is  adjusted  until  the  galvanometer  again  is  not  deflected.  T  is  then  at  once  switched  off  to  avoid 
heating  the  electromagnet  and  the  number  of  lines  of  force  read  off  direct  on  the  scale  at  S,. 

It  is  important  that  the  amount  of  air  space  when  using  test  pieces  of  various  lengths  shall  be  accurately  known 
and  this  is  effected  by  turning  the  milled  edge  of  the  disc  forwards  and  reading  off  the  graduations.  More  complete 
instructions  will  be  furnished  with  the  apparatus  if  desired. 


79 


J 


/r 

n, 

^0  HARTMANN  & 

""                                                  CXJ~                      = 

BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M.  ^ 

IK. 

Optical  Apparatus. 

Mirrors. 

Steel  magnet  mirrors 

of  the  highest  finish  anc 

true  planes. 

Diameter  in  mm 

Polished  on  one  side 

Polished  on  both  sides 

15—20 

M.  20.— 

M.  45.— 

21—25 

M.  25.— 

M.  55.— 

26—30 

M.  33.— 

M.  70.— 

If  desired  magnets 

of  other   shapes   can   be   supplied   with   circular 

polished  reflecting  surfaces. 

Thin  true  plane  mirrors,  absolutely  accurate, 

silvered. 

Diameter  in  mm 

Thickness  0.2-0.4  mm. 

Thickness  0.5—  1  mm. 

5—10 

M.     6.— 

M.     4.— 

11—15 

M.     9.— 

M.     7.— 

16—20 

M.   12.— 

M.  10.— 

21—25 

M.  18.— 

M.   15.— 

26—30 

M.  24.— 

M.  20.- 

True  plane  mirrors  from  2—5  mm  in  thickness, 

round 

per  s 

quare  centimeter  M.  1.20 

square 

1.40 

assuming  the  area  to  be  not  less  than  6 

square  centimeters. 

Special  quotations   will 

be  given   for  mirrors   smaller   than   those   above 

listed,    larger   than 

50   square    centimeters, 

or   of  greater   thickness 

than  7  mm. 

The  price  of  unsilvered 

mirrors  is  10°/o  less. 

Concave  mirrors  for 

measuring  instruments,   focus  50  cm,   0.4  mm   in 

thickness,  10,  15  and  20  mm  in  diameter  and  silvered  at  back. 

Price  M.  6.—,  9.—  and  12.— 

Concave  mirrors  for  reflecting  telescopes  in  glass  with  polished  silvered 

surface,   or   in   hard   silver   coloured   bronze 

alloy,   from  5  to  20  cm 

diameter,  will  be  specially  quoted  for. 

"L, 

J 

80 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Eye  Pieces. 

Terrestrial  Eye  Piece  Lux 

Mittenzwey  type. 

The  terrestrial  Lux  Eye  piece  is  formed  with  a  bi-convex  and  a  plano-convex 
lens,  both  achromatic,  and  covers  a  large  field  with  perfect  definition  throughout.  It 
is  well  adapted  for  direct  use  as  a  magnifying  glass,  the  great  distance  from  the  object 
being  very  advantageous. 

Equivalent  focus      .     .     .     cm  ||     3      |    2.5    |      2      |    1.5    |   1.25   |      1      |    0.8 

Length about  cm  |     18     |     15     |     12    |      9      |    7.5    |     6     |     5 

Price,  including  mountings,  M.  ||  50.—  |  42.—  |  36.—  j  30.—  {  30.—  |  30.—  |  30.— 


Astronomical  Eye  Pieces. 

Improved  Holosteric 

Huyghen  Eye  Piece  Micrometer  Eye  Piece 

Mittenzwey  type. 


The  Improved  Huyghen  Eye  piece  is  formed  with  two  simple  lenses  mounted 
at  the  requisite  distance  apart  to  ensure  achromatism;  it  covers  a  field  of  about  55° 
with  perfect  definition  throughout,  excelling  in  this  respect  the  excellent  three  lens 
Steinheil  eye  pieces;  and  is  of  great  service  as  long  focus  eye  piece  for  comet  seeking. 
Equivalent  focus  .  .  cm  ||  6  |  5  |  4  |  3  |  2  |  1.5  |  1  j  0.75  |  0.5 


Price,  mounted  in  cells')  M.  ||  30.-  |  24.-  [  18.-  |  15.-  |  12.-    10.—  |  10.—    10.—  |  12.— 

The  Holosteric  Micrometer  Eye  piece  is  formed  with  two  cemented  lenses, 
and  therefore  has  only  two  refractions,  glass -air,  it  is  quite  free  from  flare,  and 
gives  perfectly  sharp  flat  pictures  without  aberration  in  a  field  of  35°.  It  is  especially 
noticeable  for  the  great  distance  from  the  object  at  which  it  works,  16  mm  in  an  eye 
piece  of  2  cm  focus,  and  is  therefore  extremely  useful  as  an  aplanatic  magnifying  glass. 
Equivalent  focus  .  .  cm  ||  3  |  2.5  |  2  |  1.5  |  1.25  |  1 


Price,  mounted  in  cells")  M.  ||  30.—  |  25.—  |  20.—    18.-  |  18.-  |  18.— 


*)  If  these  eye  pieces  are  to  be  fitted  to  an  existing  telescope  we  desire  the  eye  piece  mount  or  a  flange  to  be 
sent  to  us  and  the  cost  of  fitting  is  extra.  The  outer  tube  for  the  holosteric  and  the  euryscopic- aplanatic  micrometer  eye 
pieces  on  page  82  are  not  included  in  the  prices  quoted,  although  shown  in  the  engravings  to  illustrate  the  great  distance 
between  lens  and  object. 


81 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Equivalent  focus 


Euryscopic-aplanatic  Micrometer  Eye  piece 

Mittenzwey  type. 

The  Euryscopic  Micrometer  Eye  piece  is  formed 
from  a  cemented  three  lens  combination  strongly  over- 
corrected  for  spherical  and  chromatic  errors  and  a  concavo- 
convex  lens  having  similar  errors  in  the  opposite  direction. 
This  system  complies  to  a  very  high  degree  with  all  the 
essentials  of  a  perfect  micrometer  eye  piece :  the  euryscopic 
and  orthoscopic  stability  of  the  achromatism,  aplanatism 
both  in  and  without  the  axis,  long  distance  between  lens 
and  object,  and  freedom  from  troublesome  reflections  render 
it  as  perfect  as  possible.  In  a  field  of  view  of  53°  the 
distance  between  lens  and  object  in  an  eye  piece  of  2  cm 
focus  is  11.5  mm. 
cm  ||  2  |  1.75  |  1:5  |  1.25  |  1  |  0.75  |  0.5 


Price,  mounted  in  cells  M.     25.-    23.—    20.—    20.-    20.-    20.-    20.- 

(see  foot  note  on  page  81)  || 

Eye  piece  cover  with  small  aperture  to  the  micrometer  eye  pieces,  for  measure- 
ments with  bright  threads  on  a  dark  ground  (according  to  Abbe)  .     .     .     Price  M.  1.50 

Ramsden  astronomical  Eye  pieces  (-2  plano-convex  lenses  in  brass  mounts, 
image  in  front  of  the  system)  of  equiv.   foci  from  0.5  to  2  cm     ....     Price  M.  9. — 

Steinheil  astronomical   Eye  pieces   (3  plano-convex   lenses  in  brass  mounts 
with  screw  type  adjustment  on  to  the  cross  threads,  image  between  the  collective  and 

second  lenses)  of  equiv.  foci  from  0.5  to  2.5  cm Price  M.  12. — 

of  equiv.  foci  of  3.0,  4.5  and  6.0  cm  Price  M.  24.—,  40.—  and  60.— 

Accurately  centered  lenses  of  any  desired  focus,  plano-convex  or  bi-convex,  plano- 
concave or  biconcave.     Prices  according  to  quantities  ordered. 

Achromatic  Object  glasses  for  telescopes 

made  up  of  two  lenses. 


Clear 
Aperture 

Focus  in  cm 

Price 
including  mount 

M. 

Clear 
Aperture 

Focus  in  cm 

Price 
including  mount 

10 
15 

20 
25 

27 
30 

8,  10,  12 
8,  10,  12 
8,  10,  15,  20 
18,  20,  25,  30 
18,  20,  25,  30 
25,  30 

6.- 

8.- 
11.— 
14. 
16.- 

18.- 

35 

40 
50 
55 
60 

70 

30,  32,  40 
32,  40,  48 
50,  55,  60 
55,  60 
60,  72 
70,  84 

24.- 
32.— 
45.- 
55.- 
70.- 
115.- 

Larger  object  glasses  with  aperture  ratio  of  1 : 12  or  1 : 15.     Prices  to  quote. 
Powerful   achromatic   object   glasses   of  very   short   focus    made   up   of 
three  lenses. 

Clear  aperture     in  mm  ||    20     |     25     |     27     |     30     |     40     |     50     |     60 


Focus . 


7.5 


9      |     12 


15 


is 


Price  ....      „      M.  ||  16.—  |  21.-  |  24.—  |  30.-  |  45.—  |  70.—  |lOO.- 
Prices  will  be  quoted  for  mounting  object  glasses  in  wood,  brass  or  steel  tubes. 


r* 

^ 

_  HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT 

A^K 

°-  M"     Q, 

Prisms. 

Prisms  in  crown  or  flint  glass  with  point 

angle  of  60°  or  any  smaller  angle  preferred, 

with  perfect  true  plane 

polished  surfaces. 

Clear  aperture 
or  leno-th  of  side 

With  2  pol  s 

hed 

With  3 

polished 

With 

2  polished 

With  3  polished 

round  surfaces 

round  surfaces 

quadratic*)  surfaces 

quadratic*)  surfaces 

10 

I 

M. 

6.- 

M.     8.- 

15 

7.- 

9.— 

20 

M.     7.- 

M. 

9.— 

9.- 

12.— 

25 

„    10.— 

„     18.— 

13.- 

17.— 

30 

,    14. 

„     18.- 

18.- 

24.— 

35 

„    19.— 

25.- 

25.- 

33.- 

40 

..    25  - 

3 

3.— 

33.- 

44.- 

45 

32- 

43.- 

43.— 

56.- 

50 

40.- 

54.— 

54.— 

72.- 

60 

60.- 

80.- 

80.— 

„  106.- 

70 

80.- 

106.- 

106.- 

„  140.- 

80 

100.- 

13 

0.- 

130.- 

„  170— 

*)  Prisms  w 

th  rectangular  surfa 

ces  wil 

be  specially 

charged  for. 

Prisms  in  quarz,  thallium  glass,  Feil's  and 

Chance's  double  extra  dense 

flint  glass,  or 

the  new  and  valuable   series 

of  Jena  glasses, 

such   as   phosphate-crown,    barium- 

phosphate 

and  borate-  crown,  borate-flint  and  silicate-flint  (with 

nD 

=  1.9626)  are 

supplied  as  cheaply  as  possible,  the  cost  varying  with  the  material 

employed. 

Rectangular 

reflection  prisms 

in  crown  glass,   perfectly  true  in  angles   and  sur- 

faces  and 

free  from  pyramidal  error. 

Clear  aperture 
or  length  of  side 

With  round 
Catheten  surfaces 

With 
rectangular 

Cathe  en  surfaces 

Clear  a 
or  length 

"oTsfde 
im 

With  round 

With 
rectangular 

3-8 

_ 

M. 

6.—**) 

45 

M.     63.- 

M.    95.- 

10 

— 

8  —  '"''*) 

50 

80.- 

„    120.- 

15 

— 

12.-**) 

60 

„    100.- 

„    150.- 

20 

M.  21.— 

27.— 

70 

„    150.— 



25 

26  

35.- 

8( 

) 

„    240.- 

. 

30 

I    32!- 

45.- 

90 

„    350.- 



35 

„    40.— 

60.- 

100 

„    500.- 

— 

40 

„    50.- 

„ 

75.- 

120 

„    800.- 

— 

**)  The  reflect  on  prisms  from 

3  to  15 

mm  in  lengt 

h    of  side  ar 

e  only    ntended    for  ligh 

ing  purposes   and  are  not 

therefore  made  with 

absolutely  accurate 

angles  : 

nd  surfaces. 

Silvering  the 

hypothenuse 

surface   of  the 

above  reflection  prisms  per 

Qcm   M.  0.20 

with  a 

minimum 

charge  of    „     1.  — 

Straight  sight  prisms,  C. 

Braun's  type. 

Aperture  in  mm  .  ||          8 

10 

15 

20 

25 

|         30 

of  3  Prisms  . 

M.  ||      15.- 

|       20.- 

30.— 

40.-             55.- 

75.- 

of  5  Prisms  . 

M.  ||      20.- 

SO.— 

45.- 

65.—            90.- 

|     120.- 

Prisms 

for  various 

purposes: 

Prisms  for  fluids,  Steinheil  pattern,  with 

air  tight  true  plane  discs,  bore 

20  and  30  mm 

M.  80.— 

and  M.  140.— 

Angle  prisms  in  holder  and  case,  length  of  side  20  and  25  mm    „      9.— 

„       „       12.— 

Combined  prisms   of  every   description 

in  exact 

accordance   with 

any   specification 

will  be  quoted  for. 

V, 

J 

HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


H-i 


r 

,  HARTMANN  &  BRAUN,  BOCKENHEIM.FRANKFORT  o.  M. 


Spectrometer. 

No.  446.  Spectrometer  with  covered  circle  12  cm  diameter.  Reading  to 
30  sec.  by  two  verniers  and  magnifying  glasses;  circle  and  observing  tube  are  inde- 
pendant  of  each  other,  can  be  rotated,  and  are  fitted  with  micrometer  adjustment;  the 
eye  draw  of  observing  tube  is  adjustable  by  rack  and  pinion  and  the  eye  piece  is  fitted 
with  a  total  reflection  prism  in  lieu  of  the  Gauss  mirror  eye  piece;  this  can  be  easily 
moved  to  one  side  after  adjustment  thereby  enabling  the  position  of  the  telescope  to 
be  frequently  checked  without  difficulty  whilst  working.  The  slot  is  fitted  with  a 
comparison  prism,  both  observing  tube  and  slot  tube  have  object  glasses  25  mm  diameter 
and  can  be  set  to  a  very  acute  angle  with  each  other,  are  easily  removed  and  quickly 
adjusted.  The  small  prism  table  can  be  regulated  for  height  and  also  to  the  minimum 
of  deflection  through  frictional  contact  by  hand  adjustment.  Price  M.  600. — 

Crystal  Holder  with  centreing  attachment  taking  the  place  of  the  small 
prism  table  and  enabling  the  spectrometer  to  be  used  as  a  goniometer.  Price  M.  50.— 

No.  454.  Eohlrausch  Total  Reflectometer  for  determining  the  light  refracting 
powers  of  solid  bodies.  The  substance  to  be  examined  can  be  either  transparent  or 
opaque  and  with  either  single  or  double  refraction  and  need  only  have  one  small  plane 
surface.  The  instrument  has  a  circle  of  10  cm  diameter  divided  into  degrees  reading 
on  the  verniers  of  the  inset  alhidade  to  3  min.  Crystal  holder  with  double  ball  and 
socket  joints,  clamp  with  disc  points,  direction  sector,  thermometer,  telescope  with  cross 
threads,  glass  micrometer,  a  second  observing  tube  with  hall  eye  lens  and  cross 
engraved  in  glass  in  lieu  of  the  object  glass,  and  black  glass  mirror  for  observations 
with  polarised  light,  shield  carrier  and  shield.  Price  M.  180. — 

No.  454  a.  Total  Reflectometer,  as  above,  but  with  circle  12  cm  in  diameter, 
graduated  in  half  degrees,  verniers  reading  to  1  min.  on  alhidade  with  micrometric 
adjustment,  magnifying  glasses  and  holders.  Price  M.  220.— 

Extras  for  Nos.  444  and  454a: 

1)  Crystal  holder  with  graduated  circle  and  verniers,  and  external  micro- 
meter screw  adjustment Price  M.  45. — 

2)  Nicol's  Prism  mounted  in  small  tube  fitting  the  telescope  support. 

Price  M.  20.— 

3)  Trough  in  flint  glass  with  parallel  glass  sides,  for  determining  the  refraction 
ratios  of  fluids '.'._.. Price  M.  15.— 

4)  Wood  case „       „   20.— 

(Wiedemann's  Annalen  IV,  1879,  page  1.) 


85 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  454.     Total-Reflectometer  (Kohlrausch). 


Va  n.  Gr. 


No.  456.  Small  Spherometer  with  three  feet  and  contact  screw,  one  plane 
and  one  spherical  glass,  suitable  for  practical  instruction.  Price  M.  55.— 

No.  466.  Small  Cathetometer,  iron  tripod  with  adjusting  screws,  steel  cylinder 
60  cm  long  with  inset  scale  on  German  silver.  Telescope  with  rack  and  pinion  adjustment 
to  eye  piece,  and  two  interchangeable  object  glasses  for  large  and  extremely  small 
distances;  with  micrometric  adjustment  for  height.  Price  M.  350.— 

No.  477.  Small  Theodolite,  for  physical  laboratory  work,  no  iron  or  steel 
employed.  Diameter  of  the  horizontal  circle  12  cm,  of  the  vertical  circle  10  cm,  reading 
to  80  sec.  Telescope  aperture  25  mm,  20  cm  focus,  eye  piece  prism,  and  sun  glass. 

Price  M.  450.- 

Photographs  of  Nos.  456,  466  unJ  477  are  at  our  clients  disposal. 


86 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  387. 
Opal  glass  Photometer. 

L.  Weber's  type. 


ca.  Ve  n.  Gr. 


No.  387.  Weber's  Opal  glass  Photometer  in  the  portable  arrangement  here 
illustrated  can  be  used  like  the  Bunsen  Photometer  to  determine  the  intensity  of  a 
source  of  light,  especially  of  arc  and  incandescent  lamps,  and  also,  without  any  extra 
apparatus,  to  determine  the  alteration  of  light  emission  in  these  lamps  at  different 
angles  of  elevation,  it  is  also  adapted  to  determine  the  degree  of  heat  in  incandescent 
lamps  (ratio  of  the  green  to  the  red  rays).  The  chief  merit  of  the  instrument  however 
is  its  ability  to  measure  the  diffused  light  in  a  room  illuminated  by  these  lamps  without 
difficulty  and  in  a  very  simple  manner,  for  which  purpose  its  extreme  portability  is  a 
great  advantage;  it  gives,  direct  in  candles  per  square  metre,  the  degree  of  illumination 
on  various  surfaces  in  a  room. 

The  standards  for  comparison  are  various  opal  glass  discs  illuminated  by  a 
benzine  lamp  fitted  with  means  for  measuring  the  height  of  flame  —  the  constants  for 
these  discs  are  determined  beforehand  and  sent  with  the  apparatus,  but  can  be 
checked  at  any  time  by  the  instrument  itself.  The  instrument  is  furnished  with 
Lummer-Brodhun  Prisms.  Price  M.  420.— 


87 


HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


No.  570. 

Standard  Photometer  with  accessories  and 
Lummer-Brodhun  Prisms. 

No.  570.  The  Standard  Photometer  comprises  two  metal  tubes  cased  with 
ebonite,  over  two  metres  long,  these,  by  means  of  two  supports  fitted  with  adjustable 
feet,  are  combined  to  form  a  very  firm  pair  of  rails,  which,  through  the  addition  of  an 
elongation  piece  and  support  can,  if  desired,  be  extended  to  a  total  length  of  somewhat 
over  three  metres.  The  front  rail  is  graduated  in  half  centimetres  with  the  part  between 
75  and  175  divided  into  millimetres,  and  the  backrail  can,  if  desired,  be  graduated  to 
read  direct  the  ratio  of  intensity  of  the  lights  under  examination.  On  these  rails  are 
three  moveable  carriages  with  tubular  clamps,  two  of  which  have  rack  and  pinion 
adjustment  to  the  tubes.  The  carriage  in  the  centre  is  fitted  with  a  reversible  photo- 
meter case  with  Lummer-Brodhun  prisms  arranged  for  the  disappearance  of  one  field 
within  the  other  (equality),  another  carriage  is  fitted  with  a  standard  amyl-acetate  lamp 
and  indicator  for  height  of  flame  (Hefner  light  =  0.88  english  sperm  candle)  whilst 
in  the  third  carriage  the  various  accessories  supplied  for  holding  the  source  of  light 
(candle  holder,  incandescent  lamp  socket,  table  for  paraffme  lamp  &c.)  can  be  inserted. 

As  above  described  with  rails  2  metres  in  length   ......  Price  M.  580.— 

Extras: 

1)  Extra  Rails  &  support  to  form  bench  of  3  metres    ......    Price  M.  70.— 

2)  Light  ratios  marked  on  back  rail     ............        „       „     25.— 

3)  Photometer  screen  -with  Lummer-Brodhun  Prisms,  for  contrast  work  (two 
fields  appearing  equal  within  the  frame  of  a  third)  suitable  also  for  equality  work. 

Price  M.  160.— 

If  this  screen  is  selected  in  lieu  of  the  other,  the  extra  cost  is  M.  30.—  the 
latter  being  charged  at  M.  130.—. 

4)  Graduated  arc  to  photometer  screen,  and  Shadow  caster  for  photometric  work 
at  any  desired  emission  angle      ..............    Price  M.    55.— 

5)  Mirror,  adjustable  in  all  planes,  with  divided  circle  and  graduated  arc        „        „    175.  — 

6)  Dispersion  lenses,  3  of  various  foci,  for  reducing  the  intensity  of  powerful  sources 
of  light,  with  stand  and  screen,   a  true  plane  glass   to   equalise   the   absorption   of 
light  in  the  material  of  the  lens  is  also  included      .......     Price  M.  65.— 

7)  Incandescent  lamp  holder  with  horizontal  and  vertical  movements  and  graduated 
circles  to  determine  amount  of  same,  for  photometric  measurements  with  the  lamp 
at  any  desired  angle    ..................  Price  M.  190.  — 

8)  Standard  Hefner  Lamp  (duplicate)  with  flame  measurer,  standard  gauge,  and  spare 
wick  tube,  with  certificate  from  the  Imperial  Phys.-Techn.  Laboratory.    Price  M.  50.— 

9)  Petroleum  lamp,  for  comparison  of  more  powerful  sources  of  light.      „      „    30.— 
10)  Amyl-acetate,  chemically  pure,  at  cost     ....   Price  per  Kilo  M.  4  to  5.— 

No.  571.  Photometer  of  a  similar  but  simpler  construction,  specially  suitable 
for  incandescent  lamp  measurements,  with  2  rails  of  angle-iron,  3  m  long,  one  of  these 
with  cm  divisions.  The  centre  stand  is  fitted  with  a  small  Photometer  screen  Lummer- 
Brodhun  system  for  equal  fields,  one  of  the  others  carries  a  Standard  Hefner  lamp, 
the  other  one  is  intended  for  the  sources  of  light  to  be  compared.  Price  M.  300.— 


J 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


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HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


X.    Technical  Measuring  Instruments 

for  continuous  or  intermittent  control  of 

electrical  installations. 


Quality 

of  material  and 
manufacture. 


Scales. 


Price. 


These   technical    measuring   instruments   are 

made  on  the  same  lines  as  our  scientific  instruments 
and  with  the  same  high  quality  of  material  and  work- 
manship throughout.  Even  externally  therefore  they 
compare  favourably  with  the  bulk  of  the  electrical 
measuring  instruments  now  on  the  market,  and  this 
comparison  is  still  more  to  their  advantage  when  those 
parts  usually  hidden  behind  the  dial  or  scale  are  ex- 
amined. To  attain  a  frictionless  adjustment  the  pointers 
are  all  mounted  in  hard  polished  jewels  and  not  in 
metal  bushes. 

We  have  attached  great  importance  to  the  pro- 
duction of  the  most  suitable  scale  in  all  our  instruments 
and  the  choice  of  the  principle  of  construction  has  been 
partly  influenced  by  our  endeavours  to  obtain  a  scale 
of  equal  divisions  throughout,  especially  suitable  for 
current  meters,  or  for  potential  meters  one  with  very 
wide  divisions  at  a  certain  part  of  the  scale.  —  (See 
pages  126  and  127.) 

In  spite  of  the  extra  cost  due  to  the  high  quality 
of  material  and  the  accuracy  of  workmanship  employed, 
it  will  be  found  that  our  prices,  owing  to  systematized 
manufacture,  compare  favourably  with  those  of  our 
competitors. 

The  ampere-  and  voltmeters  illustrated  on  pages  Rules  observed  in 
102  and  103  working  on  the  electro -magnetic  prin-  calibrating  and 
ciple  are  those  as  yet  most  employed.  To  ensure  per- 
manent accuracy  in  their  readings,  these  instruments 
are,  after  the  magnetic  properties  of  each  iron  core 
has  been  tested,  kept  in  circuit  for  a  considerable  length 
of  time.  To  reduce  the  influence  of  external  magnetic 
fields,  the  working  coils  are  wound  with  the  maximum 
number  of  ampere  turns  admissible,  and  in  the  case 
of  voltmeters  a  sufficiently  high  inductionless  resistance 
in  Constantan  is  inserted  in  series,  so  that  the  external 
temperature  affects  the  readings  but  slightly,  the  limit 
of  error  not  exceeding  that  of  .i  1  per  cent  usually 
admitted  in  technical  measuring  instruments.  Accurate 
readings  with  these  voltmeters  for  continuous  work  are 
attained  when  they  have  been  in  circuit  for  about  10 
minutes. 


adjusting 

electromagnetic 

instruments. 


91 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Mounting 
electromagnetic 

instruments 
on  Switchboards. 


Standard 

instruments  for 

direct  current, 

dead'beat. 


Hot-wire 
instruments 

for  direct 

and  alternating 

currents. 


When  mounting  electromagnetic  instruments  of 
any  description  on  a  switchboard,  it  is  essential  that 
they  be  placed  at  a  certain  distance  away  from  magnets, 
such  as  relays  and  still  more  so  from  the  dynamo  or 
from  leads  carrying  current,  the  distance  depending  on 
the  maximum  current  carried  and  whether  lead  and 
return  cables  are  side  by  side  or  only  one  cable  is 
likely  to  affect  the  readings,  in  the  latter  case  the  instru- 
ment should  not  be  nearer  to  the  cable  than  about 
'20  cm  with  a  maximum  current  of  100  amperes,  40  cm 
for  300  amperes,  50  cm  for  500  amperes  and  about 
70  cm  for  1000  amperes,  whilst  in  the  former  case  these 
distances  may  be  reduced  to  one  half.  Single  leads  do 
not  affect  the  instruments  if  they  are  fixed  behind 
the  centre  of  the  coils.  Errors  due  to  neglect  of  these 
precautions  frequently  occur,  despite  of  the  instructions 
forwarded  with  each  instrument,  but  they  can  be  reme- 
died by  exchanging  or  replacing  these  electro-magnetic 
instruments  by  the  standard  ampere-  or  voltmeters, 
page  95,  or  the  hot-wire  instruments,  page  99  all  of 
which  are  of  the  same  design  externally. 

The  standard  ampere-  and  voltmeters  with 
moving  coil  in  a  constant  magnetic  field,  for  use  with 
direct  current  only,  are,  on  account  of  their  greater 
accuracy  —  at  least  Ya  per  cent  —  most  suitable  as 
check  instruments  in  installations  where  several  volt- 
and  amperemeters  are  mounted  on  the  switchboard, 
they  are  also  dead-beat  and  therefore  extremely  well 
adapted  for  use  where  gas  engines  furnish  the  motive 
power,  still  more  do  they  compete  on  equal  terms 
as  regards  accuracy,  whilst  at  a  considerably  lower  cost, 
with  those  instruments  of  foreign  manufacture  which 
have  up  to  date  been  so  frequently  employed  where 
their  extra  cost  as  compared  with  the  total  cost  of  the 
installation  is  of  no  account: 

Hot-wire  Instruments  are  extremely  suitable 
for  use  with  both  direct  and  alternating  currents,  are 
absolutely  unaffected  from  any  external  source  and,  as 
compared  with  direct  current  electromagnetic  instruments, 
are  free  from  the  residual  magnetism  error  arising  in  the 
latter,  and  therefore  an  accuracy  of  at  least  Vs  per  cent 
is  attainable;  as  the  prices  for  these  instruments  are 
but  slightly  above  those  for  electromagnetic  instruments 
they  should  be  preferred  to  the  latter.  For  alternating 
current  they  are  superior  to  all  others  as  they  are  free 
from  self  induction  and  entirely  independant  of  the 
number  of  cycles.  The  measuring  wire  in  these  instru- 
ments is  not  damaged  by  currents  twice  as  large  as  the 
maximum  marked  on  the  scale. 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


For  installations  in  which  large  current  variations 
occur  it  would  therefore  appear  more  adviseable  to 
employ,  even  for  alternating  current,  instruments  of  the 
electromagnetic  type  as  they  would  not  be  damaged 
if  the  current  for  a  short  space  of  time  very  conside- 
rably exceeded  the  maximum  range  of  the  instrument. 
The  type  of  electromagnetic  instrument  described  on 
page  103  is  better  adapted  for  alternating  current  work 
than  any  other  electromagnetic  type  now  used,  as  the 
calibration  curves  for  both  classes  of  current  are  approxi- 
mately alike  and  the  number  of  alternations  has  practi- 
cally no  effect  on  the  readings.  *)  It  is  however  always 
preferable  when  ordering  instruments  in  which  an  iron 
core  is  employed,  for  use  with  alternating  current,  to 
state  the  number  of  cycles. 

For  electrical  installations  on  board  ships  the  use 
of  the  dead-beat  standard  voltmeter  page  95  or  the  hot- 
wire voltmeter  page  99  is  preferable  to  that  of  an 
electromagnetic  voltmeter  with  gimbal  suspension  usually 
adopted,  as  with  the  two  former  this  inconvenient 
method  of  suspension  is  unnecessary,  whilst  the  readings 
remain  accurate  owing  to  the  aperiodicity  of  these  two 
classes  of  instruments. 

The  electrostatic  voltmeter  for  high  potentials, 
page  109,  the  Ohmmeter,  page  117,  and  the  Watt- 
meter, page  118,  should  be  specially  noted;  externally 
they  are  identical  with  the  other  instruments  usually 
mounted  on  switchboards,  are  direct  reading,  and  suitable 
for  use  with  either  direct  or  alternating  current  of  any 
periodicity. 

All  our  instruments  are  carefully  tested  before 
they  leave  our  works,  and  are  only  locked  under  lead 
seal  with  lettering  H.  &  B.  when  they  correspond  with 
the  readings  of  the  check  instruments  which  have  been 
certified  by  the  Imperial  Physico-Technical  Laboratory. 
Only  in  cases  where  this  seal  is  not  damaged  and 
where  there  is  no  evidence  of  damage  arising  from 
unskilled  use  we  undertake  repairs  free  of  charge. 

In  reference  to  our  guarantee  please  refer  to  para- 
graph No.  9  on  page  V  of  the  preface. 

If  desired,  these  instruments  will  be  supplied 
stamped  and  certified  as  to  accuracy  by  the  Imperial 
Physico-Technical  Laboratory  and  the  original  documents 
delivered  with  them  upon  payment  of  the  charges  in- 
curred (from  5  to  10  M.) 


Electromagnetic 

instruments 

for  alternating 

current. 


Marine 
instruments. 


Electrostatic 
Voltmeter, 
Ohmmeter, 
Wattmeter. 


Guarantee. 


Certificate. 


*)  On  the  use  of  electromagnetic  measuring  instruments  for  alternating  current 
see  Dr.  Bruger,  Bericht  fiber  die  Verhandlungen  des  Int.  Elektrotechniker-Congresses  zu 
Frankfurt  a.  M.  1891.  Sekt.  1,  Seite  89. 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  601.     Standard  dead-beat  current 
and   potential   indicators  for   direct   current, 

for  use  as  portable  control  instruments. 


Arrangement  Xf*       ^>"";;>  Size: 

of  details  patented.  T«  \  Tfi  18x19x10  cm. 


These  Volt-  and  Amperemeters  are  based,  like  the  Weston  instruments,  on  the 
principle  of  the  Deprez-d'Arsonval  galvanometer,  resembling  therefore  those  described 
on  page  14  and  page  28  and  therefore  consist  of  a  moveable  coil,  in  this  case  pivotted 
in  jewels,  working  in  a  very  powerful  homogeneous  magnetic  field.  The  moving  parts 
are  accurately  balanced  and  the  instrument  can  therefore  be  used  in  any  position  either 
vertical  or  horizontal.  The  special  features  of  this  class  of  instrument  are  the  proportional 
scale,  extreme  sensitiveness  throughout  the  entire  range,  dead-beat  •  movement  of  the 
pointer  and  freedom  from  errors  due  to  external  currents;  for  use  as  portable  instru- 
ments they  are  mounted  in  strong  oak  case  with  handle. 

No.  601.    Combined  standard  dead-beat  current  and  potential  indicators 

for  currents  up  to  30  amperes  max.  and  for  potentials  up   to   200  volts   max.  with  any 

desired  range,  100-150  graduations  on  scale M.   225. — 

Commutator  for  above  for  two  degrees  of  sensitiveness  in  potential  measure- 
ments (e.  g.  up  to  15  in  tenths  of  a  volt  and  to  150  in  single  volts)  .  .  M.  25. — 

No.  601a.    Dead-beat  control  amperemeter  up  to  30  ampere  max. 

I.  with  any  desired  degree  of  sensitiveness M.   150. — 

II.  with  two  degrees  of  sensitiveness   (e.  g.  up  to    1.5  in  one  hundredths  of 

an  ampere  and  up  to  30  in  fifths  of  an  ampere)      •     •     •     •    M.   180. — 

No.  601b.    Dead-beat  control  voltmeter  up  to  500  volts  max. 

I.  with  any  desired  degree  of  sensitiveness M.  130. — 

II.  with  two  degrees   of  sensitiveness   (e.  g.  up  to   ICO  in   single  volts   and 
to  500  by  five  volts) M.  150. — 

III.  with  three  degrees  of  sensitiveness M.    175.- — 

Shunts    for   use    externally    with   Nos.    601    and  601a   up   to    150   amperes    and 

Additional  resistances  for  Nos.  601  and  601b  up  to  1500  volts     .   M.  40 100. 

Leather  case  with  straps M.  20.- 


*)  In  amperemeters    with    one   degree   of  sensitiveness   and   in   all   the    volt  neters   the    terminals  are  now  mounted 
inside  the  case,  they  are  therefore  inaccessible  when  the  lid  is  closed. 


94 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  6O2  and  6O3.    Standard  dead-beat 
Ammeter  and  Voltmeter  for  direct  current, 

in  circular  case  for  switchboards. 
*/4  n.  Gr. 


Patented 

arrangement  of 

details. 


Diameter 

of  brass  base 

225  mm. 


The  system  01  a  moveable  coil  in  a  magnetic  field  employed  in  No.  601  is  here 
mounted  in  a  well  got  up  circular  brass  case.  This  system  has  the  great  advantage 
over  all  electromagnetic  systems  in  which  iron  is  employed  to  measure  large  currents, 
that  it  is  unaffected  by  any  currents  in  its  proximity  and  the  results  of  residual  magnetism 
are  entirely  eliminated  and  as  the  pointer  takes  its  position  instantaneously  also  renders 
it  suitable  in  cases  where  other  instruments  owing  to  the  pulsating  character  of  the 
current  cannot  be  employed.  The  use  of  instruments  of  this  class  is  always  preferable 
where  absolutely  accurate  measurements  are  required. 

Standard  dead-beat  Ammeters,   circular  type 
with  exactly  equal  scale  divisions  from  zero. 


and  bottom  of  the 


as  in  other  ammeters. 


No.  602 

I 

II 

III 

IV            V         VI 

VII  |VIII 

For 

larger 

special 
quo- 
tation 

For  amp.  max.  . 

0.5  or  1 

2,  3  or  5 

10;  20,  30;  50  or  75 

100  or  150    200  or  250 

300 

400 

500 

Divided  in  amps. 

0.01 

0.02  and  0.05 

0.1;    0.2;    half 

single 

from  2  to  2 

from  5  to  5 

Price  in  M.    .     . 

110    |       115 

120 

140 

150 

160 

170 

180 

No.  602  a.  Similar  ammeters  but  with  the  zero  in  the  centre  of  the  scale, 
indicate  therefore  the  direction  of  the  current,  with  half  the  number  of  graduations 
for  the  above  maxima  of  ranges.  Extra  M.  5.— 


Standard  dead-beat  V 

with  very  open  scale  at  the  required 
reading  and  omitting  the  lower  values. 

oltmeters,  circular  type 
with  exactly  equal  scale  divisions 
from  zero. 

No.  603            I 

IA        II     |     IIA 

Ill 

IV 

V 

VI     I     VII 

For 
higher 
read- 
ings 
special 
quo- 
tations 

Up  to  volt  .    . 

50-75 

60-90 

90-120 

100—160 

I;3or5 

10;20&c.to50 

100  or  200 

300  or  400 

500  or  600 

Divided  in  volts 

half 

or  single  volts 

single 

0.01;0.05 

0.1  ;  0.2  or  0.5 

V,  ^d  •/, 

from  2  to  '< 

and  5  to  5 

Price  in  M.      . 

115 

115 

120 

120 

110 

115 

120 

130 

140 

No.  603  a.    Similar  voltmeters  but  with  the  zero  in  the  centre  of  the  scale, 
deflecting  therefore  in  both  directions,  with  half  the  number  of  graduations.     Extra  M.  5. — 

Commutator    to    increase    the    range    of  the   voltmeter    for  lower  tensions   by 
dividing  the  additional  resistance  placed  inside  the  instrument.  Extra  M.  30.— 


J. 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M 


No.  6O4. 

Standard  dead-beat  instruments  for  small  currents 
and  low  potentials 

in  upright  cases. 

Arrangement  of  details  patented. 


The  magnets  and  the  moveable  coil,  pivotted  in  jewels,  are  mounted  in  a  polished 
mahogany  case.  This  design  is  specially  adapted  for  medical  requirements,  though 
it  is  frequently  employed  in  telegraphic  work  to  determine  the  insulation  of  the  line 
and  the  comparative  strengths  of  the  flow  and  return  currents,  for  which  purposes  it 
is  more  convenient  than  the  differential  galvanometer  usually  employed. 

No.  604.  Standard  dead-beat  instrument,  in  upright  case  for 
small  currents,  with  any  desired  range  up  to  say  1000  milliamperes  in 
20—25  equal  divisions  on  both  sides  of  the  zero,  or  for  low  potentials 
with  any  desired  range  not  exceeding  25  volts.  Price  M.  95. — 

No.  604a.  Instrument  as  above  with  either  lever-  or  plug  switch 
and  two  ranges  for  current  and  potential  measurements  (e.  g.  to  20 
and  200  milliamperes  or  to  2,5  and  25  volts).  Price  M.  125.— 

No.  604b.  Instrument  as  above  with  either  lever-  or  plug  switch 
and  three  ranges  for  current  and  potential  measurements  (e.  g.  to  20 
milliamperes,  200  milliamperes  and  to  100  volts).  Price  M.  140.— 


"^ 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 

T~ 

No.  605a. 
Dead-beat  accumulator  cell  tester. 


Arrangement 
of  details  patented 


Diameter  of  case 

80  mm, 
depth  40  mm. 


U  n.  Gr. 


No.  605al. 


The  moveable  coil  magnetic  system  described  in  No.  601  is  here  mounted  in  a 
small  circular  case;  the  instrument  can  be  connected  to  any  desired  cell  regardless  of 
the  direction  of  the  current  as  it  deflects  to  both  sides  and  can  be  read  in  any  position. 


No.  605.    |  I.  to  3  volts  in  tenths  |  II.  to  10  volts  in  half  volts  |  III.  to  25  volts  in  single  volts 
Price  in  M.  If  56  58  t'O 


No.  605a.    Small  Standard  Milliamperemeter.  *) 

This  instrument,  which  in  every  respect  resembles  No.  605,  has  several  very 
considerable  advantages  as  compared  with  those  usually  employed  in  electropathy: 
1)  no  adjustment  to  the  magnetic  meridian  is  necessary,  2)  it  is  unaffected  by  other 
currents  in  the  neighbourhood,  3)  dead-beat  pointing,  it  therefore  gives  instantaneously 
the  correct  reading  without  vibration  even  with  the  maximum  variation  in  the  quantity 
of  current,  4)  equally  divided  scale  and  equal  degree  of  sensitiveness  throughout  the 
entire  range,  5)  is  also,  available  as  voltmeter  for  testing  single  cells  or  accumulators, 
6)  low  internal  resistance. 


No.  605a.  ||  I.  to  25  milliamp. 
Price  in  M. 


II.  to  35  milliamp.     III.  to  35  and  with  shunt  to  350  M.A. 


04 


No.  461a.    Large  Standard  medical  Milliamperemeter.41) 

The  moveable  coil  magnetic  system  described  in  No.  601  is  here  mounted  in  a 
large  polished  mahogany  case,  see  illustration  page  105,  and  has  all  the  advantages 
described  in  No.  605a;  it  is  fitted  with  a  long  pointer  moving  over  a  scale  of  16  cm 
radius,  and  the  graduations  can  be  read  at  a  distance  of  several  metres,  thus  enabling 
the  measurements  arising  from  the  application  of  the  electrodes  to  be  easily  checked. 
It  is  graduated  to  read  direct  from  1  to  20  milliamperes  and  by  means  of  a  shunt  the 
range  can  be  extended  either  10  or  20fold  as  ordered,  that  is  to  200  or  400  milliamperes. 
The  zero  is  in  the  centre  of  the  scale  and  the  instrument  can  therefore  be  usedjrre- 
spective  of  the  direction  of  the  current.  Price  M.  150.— 


*)  For  other  medical  galvanometers  see  pages  100  and  105. 


97 


r~ 

.  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  GOO.    Hot-wire  Ammeters  and  Voltmeters  for 
direct  and  alternating  current, 

for   use   as    portable    control   instruments. 


in.Gr. 


System 
patented. 


In  these  instruments  a  short  wire  of  platinum  silver  alloy  is  employed  to  carry 
the  current,  and  the  elongation  of  this  wire  arising  from  the  heating  effect  of  the  current 
is  transmitted  by  means  of  a  special  arrangement  to  a  pointer  mounted  in  jewels. 
Means  are  provided  outside  the  case  to  enable  the  pointer  to  be  brought  back  to  zero, 
should  the  necessity  for  so  doing  arise  through  overstraining  the  instrument,  this  does 
not  affect  the  graduations.  These  instruments,  compared  with  others  working  on  the 
same  principle,  absorb  but  little  current  in  the  measuring  wire  and  therefore  the  readings 
are  permanently  correct,  this  is  confirmed  by  the  results  of  a  series  of  tests  made  by 
the  Imperial  Physico-Technical  Laboratory.  A  magnetic  damping  arrangement  ensures  the 
dead-beat  action  of  the  pomter.  These  caloric  instruments  as  compared  with  all  electro- 
magnetic instruments  have  the  advantage  of  being  absolutely  unaffected  by  external 
currents,  and  can  be  used  for  either  direct  or  alternating  current  with  the  same  scale. 

No.  600.  Dead-beat  hot-wire  Ammeters  and  Voltmeters  combined, 

in  polished  oak  cases  for  currents  not  exceeding  50  amperes  and  potentials 
up  to  200  volts  max.  with   any  desired  range.  50—80  divisions  on  scale. 

M.  180.- 

If  with  commutator  to  increase  the  lower  range  of  the  scale  for 
potential  measurements;  by  dividing  the  resistance.  Extra  M.  30. — 

No.  600 a.  Dead-beat  hot-wire  Ammeter  up  to  50  amperes  max. 
as  portable  control  instrument 

I.  with  any  desired  range  of  scale M.   115. — 

II.  with  two  ranges  (e.  g.  to  3  and  30  amp.)     .     .     .      „    145. — 

No.  600b.     Dead-beat  hot-wire  Voltmeter  up  to  200  volts  max. 

I.  with  any  desired  range  of  scale M.   110. — 

II.  with  two  ranges „    140. — 

Leather  case  with  carrying  straps „      20.— 

^-i r-' 


HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


No.  598  and  599.     Hot-wire  Ammeter 
and  Voltmeter  for  direct  and  alternating  current 

in  circular  cases  for  switchboards. 

System  patented. 

No.  598.        IM         '  No.  599. 

in  fir 


Brass  base  225  mm  diameter. 

On  the  same  system  as  No.  600  but  mounted  in  a  circular  brass  case.  As  is 
well  known  the  readings  of  most  voltmeters  and  ammeters  are  affected  by  external 
magnetic  fields,  from  which  it  is  sometimes  impossible  to  fix  the  instruments  at  a 
sufficient  distance;  and  in  such  cases  it  is  advisable  to  use  these  caloric  instruments 
even  in  direct  current  installations  as  they  are  absolutely  unaffected  thereby.  They 
are  the  most  trustworthy  instruments  for  alternating  current  work  as  their  readings  are 
independant  of  the  current  curve  and  the  periodicity  of  the  installation. 

Dead-beat  hot-wire  Ammeter  in  circular  case 
with  approximately  equal  divisions  on  scale. 


No.  598. 

I 

II 

III 

IV 

V 

VI  |  VII 

VIII 

For 

For  amp.  max. 

0.3,  0.5,  or  1 

2,  3  or  5 

10,  20;  30,  50;  or  75 

100  or  150 

200 

300 

400 

500 

currents 

Divided  in  amp. 

0.05  and  0.02 

0.1  and  0.2 

V,;     Vi;     2/i 

2/x  or  •/, 

tr.  r,  to  r> 

froml 

OtolO 

fr20to20 

special 
quo- 

Price in  M.  .     . 

75 

80 

85 

85 

90 

100 

110 

120 

tations. 

The  lower  limit  of  range  i.-.  approximately  10°/0  of  the  upper. 
The  fall  of  potential    at  the  extreme  limit  varies  in  the  different  ammeters  from  0.2  to  0.3  volt. 

The  measuring  wire  stands  without  damage  double  the  normal  maximum  current  marked  on  the  instrument;  should 
the  zero  of  the  instrument  vary  through  such  overloading  the  pointer  can  be  reset 'by  means  of  the  adjusting  screw  provided 
for  this  purpose  on  the  left  hand  side  of  instrument. 


Dead-beat  hot-wii 

with  open  scale  for  J/i  volt 
at  the  required  reading. 

«e  Voltmeter  in  circular  case 
with  approximately  equally  divided  scale 
except  when  otherwise  ordered. 

No.  599.       ||  I 

IA|    II 

IIA 

Ill 

IV 

V 

VI 

VII 

1111 

»_  *""  *^3  2 

For  or  up  to  volt 

J50-75 

60-90  90-120 

100-150 

1,  3  or  5 

10,20;   30,50 

100  or  200 

300  or  400 

500 

Divided  in  volt 

below  the  required  reading 
1  from  5  to  5  and  then  in  »/i 

0.02and0.1 

half;      single 

fr.   5  to  5 

fr.  10  to  10 

fr.  20  to  20 

:£*s=jr 

lilt 

Price  in  M.      . 

The  current 

ITS 

mploy 

75  |   75 

ed  at  the  ext 

75 

75 

t  of  the  v 

75 

oltmeter  is  abou 

75 

t  0.22  -imp* 

95          100 

Commutator  to   extend   the  range  by  dividing  the  additional  resistance  of  the 
instrument.  Extra  M.  30.— 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  379  and  379a.    Spring  galvanometers 

Kohlrausch  type. 


No.  379  II. 


No.  379aIII. 


No.  379  VII. 


A  thin  soft  iron  tubular  core,  suspended  on  a  torsionless  spiral  spring  is  sucked 
into  a  solenoid.  At  the  base  is  a  projecting  rod  which  acts  as  a  guide  to  the  core 
and  at  the  same  time  exerts  a  powerful  damping  action  without  affecting  the  accuracy 
of  the  readings.  The  maximum  movement  of  the  core  is  approximately  100  mm;  the 
left  hand  side  of  the  scale  being  divided  into  millimetres  the  amount  of  movement  ot 
the  core  can  be  directly  measured,  whilst  the  right  hand  side  is  graduated  to  the 
equivalent  in  amperes.  By  means  of  various  patented  forms  of  iron  core  the  divisions 
on  the  scale  can  be  varied  to  suit  requirements. 


Spring 
galvanometer 

For  amps.  max. 

n 

II 

111 

IV 

v 

VI 

VII 
400 

VIII 

IX 

X 

0,001 
to  1 

M 

or  5 

10,  20 
40  or  60 

80,  100 
or  120 

200 

300 

500 
or  600 

700 
or  800 

1000 

No.  379      M 

Wall  pattern        M' 

- 

60 

54 

60 

110 

125 

150 

180 

250 

320 

No-3™a    M.  II    75 

on  tripod  base 

76 

70 

76 

Instruments  for 

arger  currents  can  only  be  supplied 
n  the  wall  pattern. 

The  minimum  current  shown  is  approximately  10°/o  of  the  maximum. 


*)  When   this  instrument   is  specially   supplied   for  medical   purposes    a  steel  needle  replaces    the   iron  core    and  tfr 
sc*le  is  graduated  to  read  direct  in  milliamperes;  by  plugging;  in  shunts  this  range  can  be  increased  10  or  20  fold. 
For  galvanometers  for  medical  purposes  see  pages  97  and  105. 


100 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  380  and  No.  380a. 

Small 
Spring  galvanometers. 

Patented  form  of  iron  core. 


ri.  Gr. 


No.  380.  No.  380a. 

To  fix  against  wall.  On  wood  base. 

These  instruments  are  fitted  with  patented  form  of  iron  core;  they  are  simply 
and  cheaply  made,  mounted  on  polished  mahogany  base  and  with  nickelled  scale  tube, 
they  are  suitable  for  constant  use  in  connection  with  subcircuits  of  an  installation,  as 
control  instruments  in  are  light  circuits,  as  lamp  counters,  and  for  laboratory  work. 
In  both  designs  at  the  same  price  and  with  the  following  graduations. 


No.  380  and  380  a  ||       I             II            III           IV 

V 

VI           VII         VIII 

For  amp  

0.5—2 

1—5 

2—10 

3—15 

4—20 

5—25 

6—30 

10-40 

Divided  in  amp.  .     . 

0.1 

0.2 

0.5 

single 

from  2  to  2 

Price  in  M.      ... 
The  above  a 

25.— 

nimeter 

20.- 

B,  gradu 

15.— 

ated  for 

15.— 

alternati 

15.—  1  15.- 

ng  current  .     . 

15.— 

Extra 

20.— 

M.  3.- 

No.  522. 
Current  Index. 

For   use   on    switch    boards    in    installations   with 

accumulators,  indicating  charge  and  discharge  with  the 

smallest  current;  well  finished  and  mounted  in  brass  case 

I.  for  currents  up  to  200  amperes      .     .     M.  12. — 

II.  ..   500  ..   20.— 


1/4  n.  Gr. 


101 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Electromagnetic  Ammeters. 

Patented  form  of  iron  core. 

No.  379b.  mgf  No.  379c. 

V*  n.  Gr. 


Diameter  of  brass  base  155  mm  in  the  small 
and  225  mm  in  the  larger  sizes. 

The  design  of  these  Ammeters  for  direct  current  is  the  same  as  that  of 
the  Kohlrausch  spring  galvanometer,  namely  an  iron  core  sucked  into  a  solenoid,  but 
in  this  case  a  spring  in  torsion  acts  as  the  opposing  force.  The  straight  line  motion 
is  converted  into  a  circular  one  by  a  lever  acting  on  an  axle  pivotted  in  jewels. 
A  patented  form  of  iron  core  enables  a  scale  with  equal  divisions  to  be  attained. 
These  instruments  resemble  externally  the  voltmeters  described  on  the  folloving  page 
and  they  are  of  excellent  mechanical  design  and  first  class  finish. 

No.  379b  and  379c.     Ammeters  for  direct  current 

with  approximately  equally  divided  scale. 


No.  379. 

I 

II     |     III 

IV 

V     |   VI  |  VII 

VIII 

IX 

X 

XI 

For  amp.  max. 

0.5  or  1 

2  or  5 

10,  '20;  :W 
50  or  75 

100orl50 

200or250 

300 

400 

500  or  600 

700  or  800 

1000 

2000 

Divided  in  amp. 

0.02  and 
0.05 

0.1  and 
0.2 

.'«, 

•/l°r»/i 

from5to5 

from  10  to  10 

from  20  to  20 

from  50  to  50 

Price  1  b  small  size 

65 

55 

45 

50 

55 

65 

are  not  made  in  the  sir 

all  size 

in  M.J    c  larger  size 

70 

60 

50 

55 

60 

70 

75    |      90 

130 

175 

250 

The  lower  limit  of  range  marked  is  as  a  rule  10°/0  of  the  maximum  value. 

In  many  cases  instruments  with  a  longer  vibration  period  are  preferable,  such 
as  ammeters  constructed  on  the  same  principle  as  the  voltmeters  described  on  the  next 
page :  This  type  is  suitable  for  both  alternating  and  direct  current  and  is  made  in 
both  sizes  above  described  as 

No.  379d  and  e.     Ammeters  for  direct  and  alternating  current 

in  small  (d)  and  larger  (e)  sizes  with  the  same  scales  as  above. 


No.  379. 


I    I 


III 


IV 


VI    I    VII    I  VIII  I    IX 


XI 


Price(  d  small  size   II   70 

60 

50 

55 

60 

70 

e  not  made  in  the 

small  siz( 

m  M'J   e  larger  size  |   75 

65 

55 

60 

65 

75 

80 

110    |    150 

200 

280 

Ammeters  for  larger  currents  specially  quoted  for. 

Ammeters  for  high  potential  work  exceeding  1000  volts  can  be  supplied  with  special  insulation  arrangements 
at  an  extra  cost;  we  make  in  this  case  the  leads  in  the  form  of  bolts  projecting  back  through  the  switchboard  so  that  no 
parts  carrying  current  are  accessible. 


J 


102 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Electromagnetic  Voltmeters. 

No.  381  b.  System  patented. 

V*  n.  Gr. 


No.  381c. 


Diameter  of  the  brass  base  155  mm  in  the  small 

and  225  mm  in  the  larger  sizes.  ;-:;:  :i :  ; '•'"'","  ..    : 

By  means  of  the  combined  effect  of  two  or  more  extremely  light  tubular  segments 
of  soft  iron  acting  on  each  other  it  is  possible  to  obtain  a  scale  with  very  open  graduations 
at  the  usual  working  position  or  one  with  approximately  equal  divisions  throughout  the 
entire  range.  The  hysterisis  error  is  extremely  small  owing  to  the  shortness  of  the 
magnetic  axes  in  the  iron  cores.  The  arbor  is  in  aluminium  with  steel  points  working 
in  jewels.  Externally  the  instruments  resemble  the  ammeters  described  on  the  previous 
page  and  the  instruments  are  mounted  in  well  made  and  highly  finished  cases.  These  volt- 
meters can  be  used  with  the  above  scales  for  either  direct  or  alternating  current 
of  any  periodicity,  but  are  always  calibrated  without  extra  charge  with  whichever  class 
of  current  is  desired. 

No.  381b  and  No.  381c.    Voltmeters  for  direct  current, 

No.  381  d  and  No.  381  e.    The  same  for  alternating  current, 

with  very  open  scale  for  1'i  Volt  at  the  usual  working  positon. 


No.  381. 

I 

IA 

II                        II  A 

For  volts 

50  to  75 

50  to  90  or  100 

90  to  120  or  130 

100-150  or  160 

Price 

M. 

,                   ,  <f         small 

bs|ord.=  |     size 

53 

53 

55 

55 

o*lor4f  '^r 

58 

58 

60 

60 

The  same  but  with  approximately  equally  divided  scale,  unless  otherwise  ordered. 


No.  381. 

III     1     IV 

V           VI 

VII 

VIII  IX*)  |    X 

IX       XII 

To  volts  max. 

:?  <>r  5 

10,  20  or  30 

100  or  200  300  or  400 

!  500  or  600  |    700 

800 

1000 

2000 

3000 

Divided  in  volt 

O.I 

'/••nd'/, 

from  2  to  2 

from  5  to  5 

from 

10  to  10 

from  20  to  20 

fr.50to50 

Price 
M, 

.    =         ,  g>     small 

D  t  or  a  s  |  size 

60 

60 

65 

are  no 

:  made  in  the  small  size 

Oiore|8^ 

65 

65 

70 

80 

90 

100 

125 

145 

175 

225 

•)The  additional  resistances  for  instruments  from  800  volts  upwards  are  contained  in  a  square  metal  case  25  x  25 x  6cm 
upon  which  the  instrument  is  mounted. 

Red   Pointer  for   indicating  the   normal  voltage,    greatly   facilitating  reading  at 
a  distance,  for  the  large  size  only M.  3.— 

Extension  of  range  by  switching  part  of  the  winding  in  series  or  parallel,  with 
commutator  and  two  scales 

to  double  the  range,  e.  g.  the  first  to  90  and  the  second  to  180  volts       fonly  for the\M.  30.— 
to  quadruple  the  range,  e.  g.  the  first  fr.  5  to  50 and  the  second  to  200  volts!  larger  size  j  n  40.— 


103 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  381. 


Portable  Voltmeter. 

System  patented. 

Vs  n.  Gr. 

• — -^— •- 

The  same  magnetic 
system  as  described  on 

the  previous  page  is 
here  mounted  in  a 

brass  case  which  is 
fitted  with  three  feet, 
one  of  which  is  arran- 
ged as  levelling  screw 
to  adjust  the  pointer 

to  the  zero  position. 
> 

No.  381.    Portable  Voltmeter 

with  open  scale  at  working  position.  with  approximately  equal  divisions. 


No.  381               I 

IA 

II 

II  A 

in 

IV    |     V          VI 

VII 

Range  in  volts     .  |50—  75 

50-90 

90—130 

100—150 

0.5—5 

5—25 

10—50 

20-100 

50—200 

Price  in  M.  .    .     .  |    70 

70 

70 

70 

75 

75 

75 

75 

80 

No.  381  M.  Inspector's  voltmeter,  similar  in  design  to  above,  with  two  scales; 
at  the  back  of  the  instrument  is  a  commutator  to  place  the  resistance  corresponding 
with  either  the  one  or  the  other  scale  in  series,  one  scale  is  to  90  and  the  other  to  150 
or  160  volts M.  90.- 

Lock  up  travelling  case  for  the  above „    12.— 

Commutator  to  extend  the  range  of  the  other  portable  voltmeters  No.  381  III— VII, 
with  two  scales,  e.  g.  0.5-5  and  to  25,  or  10-50  and  50—200  volts.  M.  25.— 

Marine -Voltmeter. 

No.  381  a  D.  Ship  voltmeter,  similar  prin- 
ciple to  the  above  but  with  gimbal  suspension  and 
ceiling  plate,  in  two  ranges,  I  for  65  volts,  II  for 
about  100  volts.  Price  M.  85.— 

No.  381  a W.  As  above  but  with  gimbal  sus- 
pension on  a  bracket.  M.  85. — 

Ammeters  cannot  be  supplied  to  hang  in 
gimbals,  nor  are  they  requisite  for  voltmeters  if 
those  types  of  Hot-wire  instruments  described 
on  page  99  or  the  Standard  instruments  on 
page  95  are  selected,  as  both  the  ammeters  and 
voltmeters  of  these  types  give  correct  readings  in 
any  position  and  are  therefore  unaffected  by  the 
13  Fl.  Gr.  ship  rolling  or  pitching. 

No.  381aD. 


104 


r 


0  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Simple  Volt-  and  Amperemeters 

for  low  tensions  and  small  currents. 
System  patented. 


No.  382. 


Vs  n.  Gr. 
No.  460  a. 


In  these  simple  Voltmeters  and  Ammeters  the  same  electromagnetic  principle 
is  employed  as  in  those  described  on  the  two  previous  pages,  and  the  most  important 
parts  are  of  the  same  high  class  of  workmanship;  the  arbors  for  instance  being  also 
mounted  in  jewels.  The  scales  however  are  not  so  closely  divided  and  are  so  arranged 
as  to  be  legible  at  a  considerable  distance.  The  cases  are  of  highly  polished  mahogany. 

No.  382.    Simple  Voltmeters  for  low  tensions,  with  backboard,  specially  suitable 

for  nickelplating  and  galvanoplastic  work,  in  the  following  ranges  all  at  the  same  price. 

I.  0.5-3  volts  divided  in  2/io;         III.  2—10  volts  divided  in  l}\    \ 

II.  1-5         „  „          „   5/io;        IV.  4-20     „  „         „   2A    | 


Price  M.  25.- 


No.  382 a.  The  same  instruments  in  portable  case  with  handle;  suitable  for 
cell  and  accumulator  testing,  specially  for  testing  electric  bell-,  clock-,  or  telephone  in- 
stallations, &c.,  with  the  same  ranges  as  No.  382.  Price  M.  30. — 

No.  460.  Simple  Milliamperemeters  in  portable  case  with  handle,  very 
suitable  for  medical  purposes.*)  In  the  following  ranges  all  at  the  same  price. 

I.  2-12  m.-amp.;        II.  4—20  m.-amp.;        III.  6-36  m.-amp.  M.  35.— 

No.  460  a.  The  same  instruments  with  plug  switch  to  add  shunts,  thereby 
increasing  the  range  tenfold,  that  is  to  120,  200,  and  360  milliamperes.  M.  45. — 


No.  461.    Large 
Milliamperemeter, 

Large  Milliampere- 
meter*) in  flat  polished  maho- 
gany case,  with  scale  of  16  cm 
radius  and  graduations  easily 
legible  at  a  distance  of  several 
metres.  Direct  reading  up  to 
20  milliamperes,  and  with  shunt 
in  circuit  to  either  200  or  400 
milliamperes :  direction  of  current 
does  not  affect  the  readings. 

Price  M.  150.- 


16  n.  Gr. 


For  Standard  instruments  for  medical  purposes  see  page  97. 


J 


105 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  383. 
Voltmeter  for  direct  or  alternating  current, 

large  size, 
for  main  switchboards  in  central  stations. 


Diameter 

of  the  frame  board 
40  cm. 


Diameter 

of  the  case 

35  cm. 


Ve  n.  Gr. 

For  large  electrical  installations,  especially  where  a  network  of  mains  is  fed 
from  several  different  sources,  the  use  of  a  main  potential  indicator  not  resembling  the 
other  measuring  instruments  is  advisable.  In  all  large  installations  also  it  is  desirable 
that  the  engineer  in  charge  should  be  able  to  check  the  potential  maintained  in  the 
mains,  which  is  his  chief  duty  to  keep  constant,  from  any  part  of  the  engine  room. 
This  voltmeter  complies  with  these  requirements. 

No.  383.  Voltmeter,  large  size,  in  brass  case  framed  in  a  polished 
wood  base.  Length  of  pointer  17  cm;  the  scale  is  only  graduated  for 
+  20  volts  of  the  normal  potential  so  that  the  width  of  each  division 
for  1  volt  is  about  1  cm  and  the  instrument  can  therefore  be  easily  read 
at  a  distance  of  6  to  10  metres.  The  system  employed  for  direct  current 
instruments  is  that  of  a  moveable  coil  in  a  magnetic  field  (see  page  94) 
whilst  that  used  for  alternating  current  works  on  the  caloric  principle 
(see  page  98),  our  improvements  in  both  systems  are  patented. 

The  price  is  the  same  for  both  classes  of  current  and  the  following 
potentials : 
I.  to  '200  volts  M.  200;  II.  to  500  volts  M.  225;  III.  to  1000  volts  M.  250. 

Ammeters  mounted  in  similar  large  cases  specially  quoted  for. 


106 


r 

HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  383a. 
Universal  Voltmeter  for  direct  or  alternating  current 

suitable  for  Central  Stations. 


Ve  n.  Gr. 


No  383a.  Voltmeter,  largest  size,  in  brass  case  50  cm  diameter 
framed  in  polished  walnut  base  of  53  cm  diameter.  As  in  voltmeter 
No.  383  the  entire  range  of  the  scale  is  graduated  in  30—40  divisions, 
therefore  for  15  —  20  volts  over  and  under  the  normal  potential  stated  on 
order;  each  division  for  1  volt  is  therefore  about  IVa  cm  wide  and  the 
divisions  are  so  heavily  marked  that  the  instruments  can  be  read  accurately 
from  a  distance  of  10—15  metres.  The  pointer  is  25  cm  long  and  is  so 
close  to  the  scale  that,  even  if  the  instrument  is  mounted  at  a  considerable 
height,  the  parallax  error  is  eliminated.  The  direct  current  instruments 
are  made  on  the  principle  of  the  standard  voltmeter,  and  those  for  alter- 
nating currents  on  the  hot-wire  principle.  In  both  systems  the  freedom 
from  hysterisis,  and  from  external  magnetic  influences  and  their  aperiodi- 
city  are  special  features. 

The  price  is  the  same  for  both  classes  of  current  and  the  following 
potentials  : 
I.  to200voltsM.300.-;  II.  to  500  volts  M.  325.-;  III.  to  1000  volts  M.  350.-. 

If  sufficient  time  is  allowed  the  large  voltmeters  No.  383  and  No.  383a  can  be  supplied  mounted  on  any  other  sort 
of  \vood  or  on  metal. 


107 


«  HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


No.  534.    Accumulator  cell  tester. 

Pocket  voltmeter. 


System  patented.  «  4     f  «/8   n.  Qr. 


This  pocket  instrument  is  constructed  on  the  principle  of  a  narrow 
solenoid  acting  on  a  pivotted  ring-shaped  curved  magnet,  and  resembling 
therefore  that  employed  in  those  described  on  pages  29  and  118.  Special 
care  is  taken  in  making  and  testing  the  constancy  of  the  magnet  employed. 
The  small  voltmeter  is  very  suitable  for  testing  separate  cells  in  a  battery 
of  accumulators  and  can  be  used  in  any  position.  Owing  to  its  compara- 
tively high  resistance  it  can  be  kept  in  circuit  for  some  time;  it  is  mounted 
in  ebonite  case  with  thick  glass  in  both  sides  and  fitted  in  a  pocket  case. 
I.  For  potentials  up  to  3  volts Price  M.  36. — 

II.  For  any  desired  potential  up  to  15  volts  max.   .         „       „  44. — 

For  permanent  use  in  accumulator  installations  a  stout  pointed  copper  wire  is 
clamped  under  one  terminal  and  contact  made  thereby  with  the  corresponding  pole  of 
the  accumulator;  a  flexible  cord  is  connected  with  the  other  terminal  and  contact  therewith 
to  the  other  pole  of  the  cell.  To  avoid  damaging  the  instrument  I  by  excessive  current 
it  must  never  be  connected  to  more  than  one  accumulator  cell. 

No.  503.    Hydrometer  for  Accumulators. 

Hydrometer  with  flat  container  to  determine  the  density  of  the  acid 
in  accumulators,  can  be  easily  inserted  between  the  plates  in  a  cell  and 
has  a  legible  scale  gratuated  on  one  side  to  Beaume  and  on  the  other  to 
specific  gravities.  Price  per  pair  M.  3.75 

No.  505.     Magnetic  field  explorer. 

A  magnetized  needle  is  pivotted  in  strong  framework 
so  that  it  is  free  to  move  in  any  direction  and  provided 
with  a  telescopic  handle;  this  is  a  very  practical  instrument 
for  testing  dynamos  and  as  a  pole  finder  is  more  con- 
venient than  pole  testing  paper  as  the  direction  of  current 
in  insulated  wires  can  thereby  be  ascertained  in  accor- 
dance with  Ampere's  rule.  With  leather  case. 

Price  M.  10.- 

J 
108 


vQ  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 

~~T~  ~~ 

No.  594. 
Electrostatic  Voltmeter  for  high  potentials. 


Brass  base 


225  cm  diameter. 


These  static  voltmeters  for  high  potentials  are  designed  on  the 
principle  of  the  Thomson  quadrant  electrometer,  externally  they  resemble 
the  other  types  of  instruments  in  circular  cases.  A  biscuit  shaped  needle 
moves  between  four  pairs  of  quadrant  shaped  inductors  which  are  specially 
designed  to  secure  an  approximately  proportional  scale.  Two  diametrically 
opposed  pairs  repel  the  needle  and  the  other  two  attract.  The  voltmeters 
are  suitable  for  measurements  of  direct  and  single  or  multiphase  alternating 
currents  of  any  frequency  and  also  for  static  electricity,  absorb  no  power,  are 
free  from  self-induction  and  unaffected  by  external  currents.  An  aluminium 
disc  working  between  the  poles  of  a  permanent  magnet  is  mounted  on  the 
arbor  of  the  pointer  to  render  it  dead-beat.  Easily  fusible  wires  are  fixed 
in  the  leads  to  the  quadrants  and  the  needle,  and  a  spark  gap  is  provided 
between  them  so  that  in  the  event  of  an  abnormal  rise  of  tension  a  spark 
passes  across  and  protects  the  instrument  from  damage.  All  parts  carrying 
current  are  extremely  well  insulated  from  the  case. 

Electrostatic  Voltmeter  for  high  potentials. 


No.  594.              I 

II 

III 

IV 

V 

Higher  readings 
to  10000  volts 
specially 
quoted  for. 

For  volt  max.  . 

|   1000 

2000 

3000 

4000 

5000 

Price  in  M.  . 

120.- 

150.- 

175.- 

200.- 

'225.- 

The  lowest  reading  is  approximately  10°/o  of  the  maximum  range  of  the  instruments. 
Instruments  for  intermediate  ranges  are  charged  as  for  the  next  higher  range. 


109 


HARTMANN  &  BRAUN,  BOCKENHEIM-FRANKFORT  o.  M. 


Contact  Voltmeter  for  direct  and  alternating  current 

with  patented  form  of  iron  core. 


No.  510. 
Contact  Voltmeter 

mounted  on  metal  base 

in  lock  up  cover 

of  polished  walnut. 

Prices  below. 


Size 

of  the  metal  base 
200x155  mm. 


It  intended    for   alterni 
kindly  state  number 


These  contact  voltmeters  are  made  with  frictionless  iron  core  and  air  damping  arrange- 
ment, a  very  great  movement  at  the  usual  working  pressure  being  attained  by  the  patented 
form  of  iron  core  employed.  On  this  core  platinum  contact  pieces  are  mounted  which 
if  the  pressure  varies  make  good  contact  in  either  direction,  thereby  closing  the  local 
circuit.  The  apparatus  is  especially  intended  for  working  optical  or  accoustic  signals,  and 
for  controlling  circuits  in  which  automatic  pressure  regulators  or  cell  switches  are  placed, 
the  relay  No.  511  on  the  following  page  being  sometimes  used  in  connection  therewith. 


No.  510  a. 
Contact  Volt- 
meter 

in  circular  case, 
matching  externally 
our  volt-  and  ampere- 
meters. 


Diameter  of  the  brass 
base  225  mm. 

The  front  of  case  is 

easily   removeable,  to 

allow  easy  adjustment 

of  the  platinum  tipped 

spring  contacts. 


Calibrated  with  e 

ither  direct  or  alternating  ci 

irrent  II            I 

II 

III 

IV 

For  higher 
pressures 
special 
quotations. 

For  volts  . 



.     .   1   50-75 

100-130 

250 

500 

Price  in  M. 

\    No.  610    .    . 

•     J     «- 

65.— 

_ 

— 

|    No.  510  a     -. 

•     1     «— 

65.- 

80.— 

100.- 

A  sensitiveness  of  1— 2°/«  is  necessary  to  ensure  good  contact,  a  variation  of 
Vz— l°/o  over  or  under  the  usual  normal  pressure  can  therefore  be  indicated.  The 
maximum  current  admissible  through  the  contacts  is  V2  amP-  For  optical  signals  lamps 
taking  small  current  must  be  used  or,  if  larger  currents  are  necessary,  a  relay  (see 
following  page)  must  be  inserted  in  the  circuit. 


110 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


""-S 


Relay  for  direct  and  alternating  current. 


No.  511. 


Size  of  base 
120x80  mm 


contact  voltmeter    with    adjustment    for   armature. 
Price  M.  30.— 


No.  511.     Single   relay 

For  65  or  100  volts 

By  means  of  this  relay  which  owing  to  its  high  resistance  absorbs  but  very  little 
current,  currents  up  to  2  amperes  can  be  employed  in  the  local  circuits  controlled  by 
the  contact  voltmeter. 

The  two  terminals  in  front  to  which  the  coil  windings  are  joined  are  connected  to  the  contact  voltmeter  or  source 
of  current,  the  two  at  sides  are  connected  to  the  circuit  in  which  the  large  current  is  required. 


No.  511a. 

can  be  used  in 
either  a  hori- 
zontal or  vertical 
position. 


Size  of  back 
200x155  mm 


No.  511a.  Compound  Relay  (double)  tor  contact  voltmeter,  similarly  constructed 
to  the  above,  mounted  on  metal  base  in  glass  fronted  polished  walnut  case,  for  use 
with  No.  510  (see  previous  page).  For  65  or  100  volts.  Price  M.  70.— 

No.  511b.    As  above,  but  in  circular  case  for  use  with  No.  510a.  Price  M.  80. — 

If  two  different  local  circuits  are  to  be  controlled  by  the  contact  voltmeter,  or  if 
the  direction  of  current  in  the  local  circuit  is  to  be  reversed,  when  the  pressure  is  too 
low,  from  that  employed  when  the  pressure  is  too  high,  then  two  relays  are  necessary. 
The  above  illustration  shows  the  method  of  connecting  a  compound  relay  with  a  contact 
voltmeter  and  an  optical  and  sound  alarm  signal  No.  512  II  (see  following  page). 


111 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  512. 
Signal  apparatus  with  optical  and  sound  alarms 

to  notify  pressure  variations  and  earth  contacts. 


ID 


No.  512.     Signal   apparatus    with    optical    and    sound    alarms, 

comprising  an  electric  bell  of  low  resistance  in  series  with  incandescent 
lamps,  the  latter  mounted  in  polished  walnut  wood  cases  behind  coloured 
glass.  The  apparatus  is  chielly  intended  for  use  with  the  contact  volt- 
meters illustrated  on  page  110,  to  which  it  can  be  connected  without  a 
relay  provided  that  incandescent  lamps  taking  less  than  lk  ampere  are  used. 
Made  in  three  patterns,  each  for  65  or  100  volts  (voltage  to  be  stated 
on  order). 

I.  with  one  bell  and  one  lamp Price  M.  25.— 

II.  with  one  bell  and  two  lamps,  one  of  which  is  mounted  behind 
green  and  one  behind  red  glass,  and  in  accordance  with  the 
variation  of  pressure  the  corresponding  lamp  is  lit,  the  bell  in 

either  case  continuing  to  ring Price  M.  33.— 

III.  with  two  bells  of  different  tones  and  one  lamp,  one  bell 
sounding  at  the  minimum  the  other  at  the  maximum  pressure 
permissible  whilst  the  lamp  is  lit  behind  red  glass  in  either  case. 

Price  M.  43. 

The  incandescent  lamp  holders  are  for  screw  socket  lamps. 

Earth  contact  alarm  apparatus. 

The  Signal  apparatus  No.  5121  can  also  be  employed  as  an 
earth  leakage  indicator  if  one  terminal  is  connected  to  earth  and  the 
other  either  permanently  connected  to  one  pole  or  alternately  to  the 
+  and  —  pole.  The  lamp  begins  to  glow  and  the  bell  to  ring  if  the 
insulation  resistance  falls  below  1000  ohms. 


112 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  513.    Alarm  Voltmeter 

with  patented  form  of  iron  core. 


*/4  n.  Gr. 

Case  in  polished 

walnut  wood. 


Size 

of  backboard 
36x24  cm. 


No.  513.  Alarm  Voltmeter.  In  this  instrument  the  motion  of  an  iron  core  in 
a  solenoid  through  which  the  current  is  passed,  is  transmitted  by  a  lever  to  an  arbor  fitted 
with  a  spiral  torsion  spring;  the  core  also  is  suspended  on  a  long  spiral  spring.  Owing 
to  the  core  being  mounted  between  two  springs  the  arbor  does  not  carry  its  weight 
and  therefore  the  index  pointer  assumes  the  accurate  position  at  any  part  of  the  scale. 
A  second  lever  is  mounted  on  the  arbor  which  touches  one  or  other  of  the  two  contact 
screws  fixed  on  the  right  and  left  hand,  thereby  closing  the  circuit  of  a  relay  which 
works  the  alarms;  these  latter  are  a  bell  and  lamps  which  give  red  or  green  light 
according  to  whether  the  maximum  or  minimum  pressure  permissible  has  been  exceeded. 
The  contact  point  for  minimum  pressure  is  arranged  to  be  turned  aside  from  outside 
the  case  so  that  the  pointer  may,  when  no  current  is  passing  through  the  solenoid, 
assume  its  zero  position,  both  contact  screws  can  also  be  adjusted  for  height  so  that 
the  alarm  circuit  may  be  closed  at  any  desired  pressure. 

For  65  or  100  volts  including  bell*)   and   incandescent  lamps. ¥¥)      Price  M.  175.— 

For  200"*)  volts „       „    185.- 

If  the  bell  is  not  required,  deduct „       „      12.— 


*)  In  most  cases  it  is  preferable  not  to  mount    the  bell  on  the  apparatus  but  to  fix  same   at  the  most  suitable  spot. 
")  The  lamp  sockets   are    for  Edison  screw  fittings,    and  the  lamps  are  mounted  behind  coloured  glasses;    ordinary 
clear  glass  lamps  of  5  c.  p.  (to  avoid  heating  the  apparatus)  should  therefore  be  used. 

*•')  In  this  case,   as  200  volt  lamps  are  not  always  in  stock,   another  100  volt  lamp  is  placed  in  the  alarm  circuit. 


113 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  c 


Differential  Voltmeter  for  direct  and  alternating 

current. 


UGr. 


Diameter 

No.  606.  Jtw^HllSl^i^llIi  of  the  brass  base 

155  mm. 


Differential  voltmeters  are  used  to  indicate  the  difference  in  pressure 
between  two  sources  of  current  in  the  three  wire  system  or  in  two 
machines  to  be  connected  in  parallel,  also  to  show  the  loss  in  pressure 
in  the  various  branches  of  a  system  of  mains. 

No.  606.  The  differential  Voltmeter  for  direct  current  is  made 
with  a  solenoid  having  two  separate  windings  of  equal  number  of  turns 
and  equal  resistance  through  which  the  current  flows  in  opposite  directions. 
If  the  action  of  one  coil  is  more  powerful  than  the  other  it  attracts  the 
x\  shaped  magnet  which  is  mounted  on  an  arbor  within  the  solenoid. 
The  scale  can  be  divided  into  single  volts. 

For  tensions  of  about  65  or  100  volts       ....     Price  M.  105.  — 

No.  606  a.  Caloric  differential  Voltmeter  for  direct  and  alter- 
nating current.  This  instrument  is  made  with  two  hot-wire  volt- 
meters (see  pages  98  and  99)  in  which  the  pointer  axes  are  in  the  same 
horizontal  plane  and  whose  pointers  work  in  opposite  directions  over  the 
scale.  The  scale  is  divided  from  the  centre  outwards  with  very  open 
readings  at  the  working  pressure  and  is  so  proportioned  that  the  divisions 
corresponding  thereto  are  in  the  same  radius  and  the  pointers  therefore 
at  the  usual  working  pressure  overlap.  With  the  differential  voltmeters 
Nos.  606  and  514  only  the  difference  of  pressures  can  be  determined  - 
these  instruments  indicate  direct  how  much  the  pressure  in  both  branches 
is  above  or  below  the  normal.  This  instrument  is  also  much  more 
suitable  for  other  purposes  than  those  which  are  already  calibrated  for 
some  definite  standard  pressures. 

For  the  usual  voltages     ..........     Price  M.  125.  — 


1U 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  514. 
Differential-Voltmeter  with  alarm. 

No.  514.  This  differential 
Voltmeter  with  alarm  is  used, 
like  the  one  described  on  the 
previous  page  to  measure  the 
drop  of  potential  in  leads,  to  check 
the  difference  in  pressure  on  the 
two  sides  of  a  three  wire  system,' 
for  use  when  switching  dynamos 
in  parallel  and  for  other  purposes. 

In  this  instrument  two  sole- 
noids and  not  one  as  in  the  signal 
voltmeter  No.  513  act  on  a  soft 
iron  core  suspended  between  two 
springs  the  motion  of  the  core 
being  transferred  by  a  lever  on 
to  the  pointer  arbor  in  a  similar 
manner  to  that  used  in  the  other 
instrument.  The  two  solenoids 
are  wound  with  the  same  num- 
ber of  turns  and  also  of  the  same 
resistance  and  are  mounted  so 
that  their  vertical  axes  are  in 
the  same  straight  line.  The  core 
projects  equally  into  each  of  the 

solenoids  and  is  so  magnetised  that  in  one  a  north  pole  and  in  the  other 
a  south  pole  of  equal  magnetic  force  is  produced.  On  the  least  difference 
occurring  in  the  magnetic  effect  of  either  solenoid  the  core  is  sucked 
further  into  either  the  one  or  the  other,  and  the  pointer  connected  to  the 
arbor  indicates  the  difference  of  potential  existing  at  the  terminals  of  the 
solenoids. 

The  contacts  by  which  either  one  or  the  other  of  the  two  bells  is 
actuated  through  a  relay  can  be  adjusted  to  work  at  any  desired  gra- 
duation on  the  scale.  Price  M.  175.— 


J 


115 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  608. 

Back  charge  and  current  Index  for  working 
dynamos  in  parallel. 


New  system 


Diameter  of  brass 
base  225  mm. 


When  working  dynamos  in  parallel,  each  driven  by  their  own 
engine  it  sometimes  occurs  as  is  well  known,  that  one  dynamo  drives 
the  other  as  a  motor,  if  the  speed  of  the  engine  driving  the  latter  falls 
below  the  normal.  In  working  dynamos  in  parallel  the  poles  also 
are  sometimes  reversed,  which,  when  the  machines  are  next  started 
causes  current  to  be  delivered  to  the  distributing  mains  in  the  wrong 
direction.  In  both  these  cases  the  faulty  working  of  the  machine  is  shown 
on  the  back-charge  indicator  by  a  red  disc  appearing  in  the  centre  of  a 
white  field.  The  apparatus  works  perfectly  at  about  5°/o  of  the  maximum 
current.  The  design  of  this  instrument  resembles  that  of  the  ammeter 
page  102.  but  to  answer  both  purposes  above  mentioned  the  solenoid  is 
wound  with  fine  wire  for  potential  measurement  as  well  as  the  usual 
winding  for  the  maximum  current,  and  in  lieu  of  the  soft  iron  core  a  per- 
manent magnet  is  fitted  which  is  sucked  into  the  solenoid  when  the 
current  is  flowing  in  the  right  direction  but  repelled  if  the  machines  are 
working  incorrectly.  The  general  appearance  externally  is  the  same  as 
that  of  the  other  instruments  in  circular  cases  for  switchboard  use. 

Back  charge  Indicators  for  working  pressures  up  to  130  volts 


No.  608.              Ill               IV 

v     :  vi    vii  vni 

for  larger 
currents 
special 
quotations. 

For  amp.  max.  II  30,  50,  or  75 

100  or  150 

200  or  250 

300 

400 

500 

Price  in  M.     .  |        80 

85 

90 

110 

120 

130 

116 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  612. 

Leakage  Indicator  or  Insulation  tester  for  direct  and 
alternating  current 

in  circular  case  for  switchboard. 


U.G 


System  patented. 


Diameter  of  brass 
base  225  mm. 


+ 


Practically  as  is  well  known  it  is  extremely  difficult  to  avoid  leakage  in  any  large 
system  of  mains,  but  the  loss  of  current  arising  herefrom  should  not  exceed  a  definite 
amount.  To  avoid  interference  with  the  usual  working  routine  the  insulation  resistance 
of  the  mains  should  be  constantly  checked  which  can  be  done  without  difficulty  by  this 
apparatus.  The  leakage  indicator  corresponds  externally  with  the  other  switchboard 
instruments  and  shows  the  insulation  to  earth  direct  in  ohms.  One  terminal  of  the 
instrument  is  permanently  connected  to  earth  (gas  or  water  main)  and  the  -+•  and  — 
poles  of  the  dynamo  or  mains  are  connected  to  the  other  two  terminals  and  either  can 
be  joined  through  the  instrument  to  earth  by  means  of  the  lever  at  side  of  case.  If 
any  considerable  leakage  is  present,  the  instrument  can  be  used  to  localise  the  fault. 


Leakage  Indicators  for  direct  and  alternating  current. 
No.  612.  I  II  III          IV  =       V  VI          VII     '     VIII    !     IX 


ApFOMmtte^tension    ||65_75 

100-125 

200 

300-400 

500-600J  700-800 

1000 

2000 

3000 

Range  in  ohms    ^^ 

100000 
to  300 

200000 
to  500 

400000 
to  2000 

600000 
to  10000 

800000 

to  20000 

1  megohm 

to  30000 

3  megohms 

to!50000 

4  megohms 

toSOOOOO 

Price  in  M.      .  j|70.— 

70.— 

70.- 

90.- 

95.— 

100.— 

110.- 

120.- 

150.— 

The  readings  of  the  pointer  are  only  correct  at  a  certain  working  pressure,  which 
must  therefore  be  stated  on  the  order,  but  slight  variations  have  only  an  inappreciable 
effect  on  the  result. 

If  both  poles  are  earthed  the  readings  shown  are  somewhat  too  high,  and  if  is  desired  to  accurately  determine  the 
amount  of  leakage  the  following  formula  must  be  used.  Let  Ct  -f  =  the  reading  of  the  instrument  when  the  lever  is  on  -J- 
and  O —  when  the  lever  is  on  —  then  the  leakage  to  earth  on  the  +  pole  is  W  i  and  that  on  the  —  pole  W — ,  when 
\V  represents  the  resistance  of  the  instrument 

w+  =  a_  _  *  ("  +  «-)   -nd   w_      -  •        w  (UJ  +  a+) 


a+ 


w  -}-  a— 


117 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  610.    Direct  reading  Wattmeter  for  direct  and 
alternating  current 

in  circular  case  for  switchboard. 


n.Gr. 


System 
patented. 


Diameter 

of 

brass  base 
225  mm 


This  instrument  is  constructed  on  the  same  electrodynamic  principle  as  Nos.  531 
to  533  page  29  without  using  iron,  and  reading  direct  on  an  approximately  equally  divided 
scale.  The  silk  fibre  suspension  there  employed  is  replaced  in  this  instrument  by  a 
horizontal  arbor  pivotted  in  jewels  and  a  very  efficient  air  damping  arrangement  which 
renders  the  pointer  practically  dead-beat  is  substituted  for  the  magnetic  damper.  The 
moving  part  is  provided  with  an  astatization  coil  as  well  as  the  working  coil  so  that 
external  fields  but  slightly  affect  the  position  of  the  pointer.  As  counter  force  is 
employed  either  a  spiral  spring  or  according  to  our  new  patent  a  quartz  fibre.  It  is 
especially  suitable  to  determine  the  watts  absorbed  by  incandescent  lamps  whilst  taking 
photometric  measurements  and  for  alternating  current  installations  where  the  direct 
reading  and  quickness  in  action  are  great  advantages.  The  instrument  externally 
resembles  our  other  circular  cased  instruments  but  the  terminals  for  the  main  current 
are  at  the  sides  of  the  case  and  not  vertically  arranged. 

Wattmeters  arranged  for  a  maximum  potential*)  of  100  volts. 


No.  610    li      I 

II 

III 

IV 

V 

vr*) 

VII 

VIII 

IX 

F.  amp.  max.  |       5 

10 

25 

50 

75 

100 

150 

200 

250 

Kilowatt          0.5 

1 

2.5 

5 

7.5 

10 

15 

20 

25 

Price  in  M.     170.- 

170.- 

170.- 

180.- 

190.- 

250.- 

270.- 

290.- 

310.- 

No.  610  a.  As  above,  but  arranged  for  a  maximum  potential  of 
150  volts  (i.  e.  for  tensions  exceeding  100  volts)  .  .  .  Extra  M.  10. — 

Resistances  in  separate  cases  for  use  in  series  with  No.  610,  with 
all  accessible  parts  carrying  current  cased  in  insulating  material,  for 
maxima  potentials 

of  500  volts  M.  75.-;    1000  volts  M.  100.—;   2000  volts  M.  200.—. 

Series  resistances  for  higher  potentials  and  Shunt  resistances  for 
currents  exceeding  250  amperes  specially  quoted  for. 

*)  Kindly  state  working  pressure  and  maximum  current  or  quote  roman  number  when  ordering1. 
**)  Shunts  for  currents  of  and  exceeding  100  amperes  are  mounted  in  a  special  case. 


118 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  543. 
Electrodynamic  spring  balance  for  the  zero  method. 

(Wattmeter.) 


-JnGr. 


The  moving  coil  of  the  Electrodynamo- 
meter  is  mounted  to  turn  easily  within 
the  main  solenoid,  a  long  but  rigid  alu- 
minium pointer  with  its  point  working 
over  a  marked  mirror  renders  it  easily 
adjusted  to  zero ;  two  stops,  between  which 
a  lever  connected  to  the  moving  coil  plays, 
prevent  the  pointer  moving  too  far  from 
zero  in  either  direction,  on  the  end  of 
this  lever  a  horizontal  disc  is  mounted 
which  dips  into  an  easily  removeable  cup 
filled  with  fluid,  thereby  causing  a  very 
efficient  damping  action.  The  movement 
of  the  coil  when  deflected  by  the  current 
is  opposed  by  a  spiral  spring  in  which 
the  extension  is  directly  proportional  to 
the  intensity  of  the  current.  The  wire 
carrying  this  spring  is,  as  in  other  known 
torsion  instruments,  wound  on  a  cylinder, 
thereby  extending  the  spring  until  the 
pointer  again  attains  the  zero  position. 
The  reading  obtained  on  the  graduated 
circle  of  the  cylinder  is  multiplied  by  a 
predetermined  constant. 

To  afford  a  wide  range  the  windings 
of  the  main  coil  of  the  electrodynamo- 
meter,  which  is  chiefly  made  as  a  watt- 
meter and  especially  suitable  for  calibra- 
ting meters,  is  wound  in  two  halves,  so 
that,  using  the  suitable  terminals,  the  two 
windings  can  be  connected  either  in  pa- 
rallel or  series.  By  means  of  a  commu- 
tator resistances  for  medium  pressures 
of  50,  100  or  200  volts  can  be  coupled  in  series  with  the  moveable  coil. 

The  apparatus,  which  is  suitable  for  use  with  both  alternating  and 
direct  current,  is  mounted  in  a  glass  fronted  polished  walnut  wood  case 
and  the  measurements  are  made  without  opening  the  front. 

No.  543.    Electrodynamic  spring  balance  (Wattmeter) 

I.  for  currents  up  to     50  amps M.  250. — 

II.    .          .          ,    ,,   200      ,, 300.- 

Instruments  for  other  currents  and  potentials  specially  quoted  for. 


Backboard  55  X  25  cm. 


119 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  537  and  538.    Recording  Ammeter 
and  Voltmeter  for  direct  and  alternating  current. 

These  recording  voltmeters 
and  ammeters  consist  of  a  tho- 
roughly damped  Kohlrausch  galvano- 
meter in  which  a  pen  is  combined 
with  the  index,  and  a  drum  driven 
by  clockwork  on  which  a  paper 
strip  with  time  divisions  can  be 
fixed.  The  Kohlrausch  galvano- 
meter is  specially  suitable  for  this 
class  of  work  as  the  amount  of 
power  it  exerts  is  sufficient  to  ob- 
viate any  question  of  the  friction 
of  the  pen  causing  inaccuracies  in 
the  readings;  a  screw  adjustment 
is  provided  to  enable  the  pressure 
of  the  pen  on  the  paper  to  be  ad- 
justed with  the  greatest  nicety  and 
the  core  can  be  regulated  to  hang 
perfectly  free  from  friction  on  a 
thin  stretched  wire  in  the  solenoid 
by  means  of  adjusting  screws  and 
a  plummet. 

The  clockwork  concealed  in 
the  drum  is  usually  arranged  for 
a  24  hours  reading,  but  if  desired, 
the  drum  can,  without  extra  charge, 
be  arranged  to  revolve  once  in  seven 
days  or  at  any  other  desired  speed. 

The  cases  are  made  in  polished 
walnut  with  lock  up  glass  fronts. 

No.  537.     Recording  Ammeters  for  dir e ct  current. 


No.537and537a*)||   II 

III             IV 

v     !  vi  |  vii      vm         ix       x 

For  amps.  max.   . 

5 

10,20,30,50 
or  75 

100  or  130 

200or25o|  300 

400 

500  or  600 

700  or  800 

1000 

Price  in  M.  .    .     . 
No.  538 

270 
.     B 

260.- 

ecordii 

260.- 

ig  Volti 

310.—      320 
neters  for  ( 

330 

lire 

340.-       380.- 

ct  c  urrent. 

475 

No.538and538a*)||      II 


ill 


IV 


VI 


VII 


VIII 


X 


For  i.  e.  up  to  volts     50-75  j  90—1 


100 


300 
or  400 


500 
or  600 


700 
or  800 


Price  in  M.  .     .     .     275.-  |  275.— 1 275    275    300.—  |  325.—     350.-      375.-     420- 

Nos.  539   and  539 a*).     Combined   Recording   Ampere-   and  Voltmeter, 

in  one  case   and  recording   on  one  drum;   the   price   is  then   reduced   from   the  total 

amount  of  the  resp.  prices  of  Nos.  537  and  538  together  by M.  50. — 

Blanks    with   time   divisions    per   100   M.    2.—.       Spare -Pens    each   M.    5.— 
Attachment    for   Recording    Ammeters    in    accumulator    installations,    in- 
dicating the  time  occupied  in  charging.  Extra  M.  30.— 

*)  The  numbers  marked  with  a  are  for  alternating  current  instrument?. 


120 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  54O.    Electrical  Meter  (watthour  Meter) 
for  direct  and  alternating  current. 

These  Watthour  meters  with  inter-  System  Patented- 

mittent  registration  consist  of  an  electro- 
dynamic  balance  on  the  same  principle 
as  that  described  on  page  117,  a  very 
simple  electrically  driven  train  of  wheel 
work  and  a  counting  gear  with  electro- 
magnet. The  train  of  wheels  act  at  regular 
intervals  on  the  spiral  spring  which  opposes 
the  motion  of  the  wattmeter  coil,  winding 
the  suspension  wire  thereof  over  a  roller  and 
afterwards  unrolling  same.  At  the  moment 
that  this  action  commences  the  counting 
gear  is  connected  by  an  electromagnet  with 
the  roller  and  this  connection  is  maintained 
until  the  spiral  spring  and  wattmeter  coil 
are  balanced,  that  is  until  the  latter  has 
been  brought  back  to  its  zero  position, 
directly  this  occurs  no  current  passes 
through  the  electromagnet  and  the  counting 
gear  is  disconnected  from  the  roller  by  a 
suitable  spring.  The  amount  the  spring- 
is  extended  and  the  counting  gear  advanced 
is  exactly  proportional  to  the  power  passing 
through  the  wattmeter. 

To  render  the  meter  more  compact 
a  balance  with  sliding  weight  in  lieu  of 
the  electrodynamic  balance  is  fitted.  In 
the  alternating  current  pattern  a  hot-wire 
instead  of  the  electromagnet  serves  to  put 
the  counting  gear  in  action. 

As  there  are  no  loose  parts  to 
be  removed  for  travelling  as  well  as  no 
means  of  stopping  the  moving  parts 
from  outside  the  case  the  counter  can 
be  passed  by  the  authorities.  The 
various  parts  are  mounted  on  a  polished 

walnut  wood  base  and  protected  by  a  sheet   metal    case   which   can  be 
closed  by  a  lead  seal  or  otherwise  fastened   after  calibration   if  desired. 

No.  541.    Watthour  Meters  for  direct  current. 


No.  541 


II      III 


IV 


vi  I  vn 


Up  to  amps  max. 

15 

25 

50 

75 

100 

200 

300 

400 

500 

Price  M.     .    .    . 

125 

130 

140  j  160 

180   !   200 

250      275 

300 

vm   *»*  **»«**"« 

1     I  system    the   extra 
cost  of  instruments 

for  the  same 
current  is  from 
M.  30  to  50.-, 


No.  541a.  Watthour  Meters  for  alternating  current  for  the 
same  number  of  amperes  are  supplied  at  the  same  prices  as  direct  current 
instruments. 


121 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 

* 


No.  544. 

Electrical  Time  Meter  for  direct  and 
alternating  current. 


Diameter 
of  base 
1GO  mm. 


Metal  cover  is 

indicated 
in  the  woodcut. 


Tn.Gr. 

In  a  great  number  of  instances  where  the  same  amount  of  current  is  always 
taken  from  a  central  station  the  use  of  the  more  expensive  meters  such  as  amperehour 
or  volt  coulomb  meters  can  be  avoided  by  substituting  a  time  meter  which  registers 
the  number  of  hours  during  which  energy  is  consumed.  The  use  of  such  simple  meters 
should  induce  a  large  number  of  users  of  a  small  but  definite  number  of  lamps  to  be 
connected  to  a  central  station  supply  who  at  present  do  not  apply  on  account  of  the 
comparatively  excessive  cost  of  meter  rental  in  comparison  with  their  outlay  for  current, 
whilst  the  possibility  of  more  current  than  agreed  for  being  fraudulently  obtained  can 
be  prevented  by  suitable  fuses  or  preferably  by  the  use  of  the  automatic  switch  de- 
scribed on  the  next  page. 

These  Time  Meters  are  also  well  adapted  to  determine  the  current  absorbed  by 
motors  intermittantly  in  circuit,  to  determine  the  amount  of  discount  allowable  for  current 
consumed  for  motive  purposes,  to  check  the  number  of  hours  lamps  have  been  lit  in 
railway  carriages,  or  that  electrical  launches  have  been  at  work. 

As  compared  with  the  time  meters  hitherto  employed  with  spring  driven  clock- 
work and  electrical  starting  and  stopping  gear  to  the  pendulum,  these  time  meters 
have  the  great  advantage  of  absolutely  electrically  driven  clockwork  which  is  quite 
unaffected  by  shocks  or  alterations  of  position  such  as  occur  in  conveyances.  The  dials 
are  graduated  up  to  1000  hours  direct  to  5  minutes,  and  the  terminals  are  so  arranged  in 
the  polished  walnut  wood  base  that  they  cannot  be  got  at  to  short  circuit  them  and  so 
cut  the  meter  out  of  circuit.  The  metal  cover  is  fitted  with  means  to  insert  a  lead  seal. 

No.  544.  Electrical  Time  Meter  for  direct  current  at  the  usual  working 
pressures') M.  38. — 

No.  544  a.    The  same   for  alternating  current  at  the  usual  working  pressures. 


*)  The  working  pressure  it  to  be  stated  on  order. 


122 


HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


No.  527. 

Automatic  Double  Cut  out  for  direct  and 
alternating  current. 


l/5  n.  Gr. 


System 
patented. 


In  small  central  stations,  more  especially  in  those  driven  by  water  power  and  in 
which  therefore  the  cost  of  generating  the  current  does  not  vary  with  the  demand  but 
is  always  equivalent  to  the  cost  of  the  maximum  output,  current  is  frequently  supplied 
for  a  certain  contract  sum  instead  of  by  meter,  and  the  contract  price  is  principally 
based  on  the  maximum  demand  and  not  on  the  time  it  is  required  per  day.  The  use 
of  the  main  switch  here  described  is  advisable  to  prevent  users  exceeding  the  stipulated 
maximum  current  by  extending  their  installation  without  notice. 

This  self  acting  Double  Cut  out  comprises  a  spring  galvanometer  in  which  the 
core  acts  on  one  arm  of  an  excentrically  pivotted  lever,  a  flat  spring  strip  bearing 
against  the  other  arm;  this  strip  is  fitted  with  a  catch  which  keeps  the  switch  block 
between  its  spring  contacts,  if  the  iron  core  is  drawn  so  deeply  into  the  solenoid  that 
the  flat  spring  looses  its  support  thereby  disengaging  the  catch  from  the  switch  block 
the  latter  flies  back  under  the  action  of  a  spiral  spring.  Another  lever  is  provided  by 
which  the  switch  block  can  be  replaced  in  position  after  the  cause  for  the  increased 
demand  for  current  has  been  removed;  this  lever  is  so  arranged  that  it  is  impossible 
to  put  the  automatic  action  out  of  gear  by  its  use. 

The  apparatus  is  contained  in  a  polished  walnut  wood  case  and  is  also  an 
excellent  substitute  for  the  main  fuses,  it  can  be  adjusted,  in  position,  'within  fairly  wide 
limits,  locked  and  lead  sealed,  and  works  with  certainty  within  +_  l°/o. 

No.  527.     Automatic  Double  Cut  out  for  direct  current. 


No.  527  and  527a 


II 


III 


IV 


VI 


VII 


For  amps.  max.  .     . 

2 

5 

10            15 

20 

25 

30 

40 

Price  in  M.      ... 

45.- 

44.  

42.-       42.- 

42.- 

44.— 

46.- 

50.- 

No.  627 a.     The  above  switch  for  alternating  current  at  the 
same  price. 


123 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


n.  Gr. 


Detector  Galvanometers. 

No.  364. 
Vertical  Detector. 

No.  364.  Vertical  detector  in  polished  maho- 
gany case  with  semicircular  magnet  resting  on  knife 
edges  the  magnet  poles  projecting  into  coils,  it  can 
be  used  in  any  position  as  regards  the  meridian  and 
is  fitted  with  travelling  stop  and  controlling  magnet. 
Resistance  about  10  ohms. 

Sensitiveness  1°  deflection  =  approx.  0.00004  amp. 

Price  M.  32.— 

No.  365.    Vertical  astatic 
Galvanometer. 

No.  365.   Vertical  astatic  galvanometer. 

(Differential)  Braun's  type.  A  horse  shoe  magnet 
made  from  steel  tube  is  mounted  at  one  end  of 
a  very  sensitive  balancebeam  with  its  poles 
projecting  into  two  solenoids  the  winding  on 
which  can  be  coupled  externally  as  desired;  it 


is  quick  in  action  owing  to  a  very  effectual 
air  damper  fixed  at  the  other  end  of  the  beam.  Safe  travelling  stop.  For 
use  in  any  position  as  regards  the  meridian.  Total  Resistance  about  100  ohms. 
Sensitiveness  1°  deflection  =  approx.  0.000005  ampere.  Price  M.  65.  — 

No.  515.    Vertical  Detector. 

(German  Post  Office  type.). 
No.  515.  Vertical  detector  with  A  shaped  magnet 
mounted  in    centres   on  palisander  wood  base   with 
solid  brass   case  and    scale  etched  on  glass,   in  two 
forms: 

I.  Of  about  20  ohms  resistance.    Price  M.  18.  — 
II.  Of  about  700  ohms  resistance.    Price  M.  25.— 
Sensitiveness   with   the  higher  resistance:    1°  de- 
flection (Vio  division)  =  0.00000  ampere. 


No.  516.  Horizontal  detector 

(Swiss  type) 

much  used  in  telegraph  work;  ///'shaped 
magnet  supported  on  needle  point,  with 
travelling  stop,  for  convenient  adjustment 
to  the  meridian  can  be  turned  in  the 
mahogany  base.  Two  turns  of  thick 
and  several  turns  of  thin  wire  of  about 

i    r         — —  1  ohm  furnish  two  degrees  of  sensitive- 

w  ****•  ness.     With  the  latter  in  circuit  l°^de- 

flection'represents  approx.  0.0001  ampere.  Price  M.  45. — 


124 


Q. 

O 
O 


125 


126 


127 


r 


~  HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


XL    Switches. 

No.  520.    Commutator  switch  to  Switch  in  series 

or  parallel. 

;i;;;;;i;;!!ijiJ!!iiii|iii!!i!!!ii!!il  I  •-;-•  V.^::::-^:,:-,. 


No.  520.  This  Commutator  is  for  use  in  accumulator  installations 
to  couple  two  halves  of  a  battery  in  parallel  when  charging,  and  when 
charged,  in  series.  It  is  also  suitable  for  changing  the  source  of  current 
in  measurements,  and  inserting  shunts  in  the  circuits  of  instruments. 
Mounted  on  lacquered  cast  iron  base.  For  currents  up  to  100  amperes. 

Price  M.  00.- 

Automatic  Switches  of  various  designs. 

Apparatus  of  this  class  are  made  for  the  most  diverse  purposes  and 
sometimes  to  carry  very  large  currents,  such  as  an  automatic  switch  to 
insert  a  shunt  to  carry  1000  amperes  with  a  recording  ammeter  for  400 
amperes.  The  release  of  a  weight  acting  by  gravity  to  insert  the  shunt 
between  the  contact  springs  with  a  total  contact  surface  of  10000  square 
millimetres  is  effected  within  an  accuracy  of  1—2  per  cent  on  attaining 
the  maximum  current  in  the  measuring  instrument. 

This  and  other  similar  classes  of  switching  apparatus  specially 
quoted  for. 

Another  automatic  switch  has  already  been  described  on  page  123. 
This  Double  Cut  out  when  used  instead  of  lead  fuses  has  the  advan- 
tage that  when  the  circuit  has  been  broken  through  overloading  it  can 
be  at  once  remade  and  further  that  the  break  occurs  if  the  •  desired 
maximum  current  is  exceeded  by  1  —  2  per  cent.  The  extra  cost  of  this 
switch  is  hardly  worth  consideration  when  compared  with  the  advantages 
it  offers,  and  this  extra  cost  is  quickly  saved  by  the  economy  in 
material  and  labour  arising  from  not  having  to  replace  blown  fuses. 


128 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  521  and  No.  521a.    Automatic  Switches 
(cut-outs)  for  maximum  and  minimum  current. 


in.Gr. 


No.  521. 


No.  521a. 


These  automatic  cut-outs,  intended  chiefly  for  use  in  accumulator  in- 
stallations, are  mounted  on  lacquered  cast  iron  bases.  The  switch  lever 
is  fitted  with  a  copper  blade  which  works  sweetly  in  contact  between 
several  copper  spring  strips  of  which  the  superficial  area  is  large  enough 
to  ensure  very  slight  friction  in  the  contacts  at  the  rated  carrying 
capacity,  a  catch  keeps  it  in  position  between  the  contacts  whilst  a  spiral 
spring  withdraws  it. 

No.  521.  Automatic  cut-out  for  maximum  current.  The  release 
of  the  catch  holding  the  lever  in  position,  when  the  maximum  admissible 
current  is  exceeded,  is  effected  by  the  movement  of  the  armature  towards 
the  electromagnet;  this  can  be  adjusted  to  within  2  per  cent  for  any 
desired  maximum  within  the  ranges  given  below. 

No.  521  a.  Automatic  cut-out  for  minimum  current.  The  per- 
manently magnetised  steel  armature  falls  directly  no  current  is  passing 
through  the  electromagnet  or  one  is  passing  in  the  reverse  direction,  and 
in  falling  releases  the  catch  holding  the  switch  lever  in  position. 

Both  types  are  supplied  at  the  same  price  to  carry  the  following 
currents. 


Nos.  521  and  521  a 


III 


IV 


V 


To  amp  

20,  30,  50  or  75 

100  or  150 

200  or  250 

Price  in  M  

75.— 

75.— 

95.— 

129 


0  HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


Simple  Cell  Switches. 

No.  523.    Cell  switch  with  screw  traverse 
mounted  on  lacquered  cast  iron  base;  the  sliding 
„    contact  has  spring  contacts  which  are  fitted  with 
intermediate  resistance,  it  has  sufficient  area  to 
I   carry   the  maximum   current  and    moves    in   a 
I   straight  line.    It  is  actuated  by  a  quick  pitched 
I   screw  which  can  be  used  either  horizontally  or 
I   vertically.     Besides   taking  up   less   room    this 
j   arrangement  enables  the  leads  to  the  various  cells 
1    to  be  arranged  in  the  most  convenient  manner. 

I  For  currents  up  to  50  amperes 
for         G  9  12  15          cells. 


M.     85.—     90.—    100.—    120.—. 

II  For  currents  up  to  100  amperes 
for       6  8  10     cells 

M.    90.—       100.—         135.— 

For   any  intermediate   number  of  cells  the 
IHHP?     next  higher  price  is  charged. 

Double  cell  switches.     Prices  specially  quoted. 

No. 524.  Instantaneous  cell  switch 

in  which  pressure  on  lever  B  causes 
the  rubbing  contact  mounted  on  a 
spring  case  with  toothed  wheel  to 
advance  one  tooth  i.  e.  on  to  the  next 
contact  thereby  putting  another  cell  in 
circuit.  Switching  off  is  effected  by 
turning  the  lever  A  backwards.  In 
this  arrangement  it  is  impossible  for 
the  rubbing  contact  to  remain  in  po- 
sition  between  two  contact  plates. 

For  currents  up  to  100  amperes  for  7  cells M.  55. — 

For  each  extra  cell,  to  11  cells „     3. — 


/  5  n  G  p. 


130 


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131 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


XII.    Apparatus  and  Material 
for  Wiring-contractors  and  -inspectors. 

No.  621. 

Portable  Ammeters,  Voltmeters  &c.,  for  wiremen 
and  inspectors. 


Size  of  portable  llRfx      -  ^^>^    '    ..«•  >  25x25x12 

case :  '       ™'I=J==~M|      ^"  *---?-;'  \     ^n  centimetres. 


To  enable  the  cheaper  electromagnetic  instruments  shown  on  pages 
102  and  103  or  any  other  instrument  mounted  in  circular  case  with  base 
of  225  mm  diameter,  such  as  the  Leakage  Indicator  page  117  or  the 
Wattmeter  page  118  to  be  used  as  portable  instruments  for  installation 
purposes,  we  supply  them  mounted  in  solid  oak  cases  with  handle.  These 
cases  are  fitted  with  lock  up  fronts  opening  downwards  so  that  the  scale 
can  be  easily  read,  and  to  render  the  comparatively  narrow  cases  firm  in 
use  without  affecting  their  portability  the  bases  are  fitted  with  adjustable 
metal  feet,  one  of  which  has  a  regulating  screw  attached  with  which  the 
pointer  can  be  brought  to  zero  on  the  scale. 

Portable  case  for  Ammeter,  not  suitable  for  currents  exceeding 
150  amperes.  The  terminals  projecting  beyond  the  circular  case  are 
removed  and  others  projecting  through  the  back  of  the  wooden  case  are 
substituted;  the  coupling  screws  are  provided  for  inside  same. 

Price  M.  30.— 

No.  621a.    Portable  case  for  Voltmeter.  Price  M.  25.— 

Other  portable  instruments, 

on  the  Deprez  principle  see  page     94, 

„      „     caloric          „  „        „         98, 

„     electromagnetic  principle  „        „       104. 


132 


No.  384c.    Insulation  Tester  for  Wiremen 

Tn.Gr. 


Size 

of  case: 


24x20x18 
centimetres. 


In  testing  the  insulation  resistance  of  small  installations  such  as  house  wiring, 
the  use  of  apparatus  fitted  with  a  magneto  inductor  is  far  preferable  to  those  depending 
on  a  few  dry  cells  to  furnish  the  requisite  current,  as  the  E.  M.  F.  of  the  inductor 
approximates  the  pressure  at  which  the  installation  will  be  worked,  whilst  cells  occupying 
the  same  space  would  not  furnish  more  than  20  volts  and  would  gradually  decrease  in 
power;  the  inductor  on  the  contracy  remains  constant. 

The  following  apparatus  contain  magnetos  for  about  100  volts,  partly  with  bell, 
partly  with  galvanoscop,  in  solid  oak  cases  with  handle;  the  crank  is  to  take  oft'  and 
to  place  inside  the  case. 

No.  384 a.  Simple  Insulation  tester  with  bells.  The  apparatus 
contains  an  alternating  current  magneto  which  rings  the  polarised  bells 
through  a  resistance  of  25  —  30000  ohms.  Price  M.  50. — 

No.  384b.  Insulation  tester  with  detector  to  approximately  de- 
termine the  amount  of  resistance  in  ohms;  comprising  a  direct  current 
magneto,  a  detector  No.  515  page  124,  and  a  comparative  resistance  of 
20000  ohms  which  can  be  inserted  by  means  of  a  switch.  The  detector 
is  calibrated  to  indicate  correctly  when  the  handle  is  turned  at  the  rate  of 
not  quite  3  revolutions  per  second  (the  military  quick  pace*)  —  and  measures 
resistances  from  10  to  over  100000  ohms  within  5000  ohms.  Price  M.  75. — 

No.  384c.  Combined  Insulation  tester  with  bells  and  detector. 
The  two  instruments  above  mentioned  are  here  combined  in  one  with 
a  magneto  for  both  alternating  and  direct  current;  two  pairs  of  terminals 
are  therefore  fitted  of  which  one  pair  W  is  for  testing  insulation  by  sound- 
ing the  bells  and  the  other  pair  G  for  use  with  the  detector.  Price  M.  100.— 


*)  Experiments   have   proved  that  most  people   are  able   to  maintain   this  speed  within   a  few   per  cent. 
The  comparative  resistance  affords  a  ready  means  of  determining  the  correct  speed,    as   when   switched   into  cir 
whilst  turning  the  magneto  the  pointer  of  detector  must  show  20000  ohms. 


133 


HARTMANN  &  BRAUN,  BOCKENHEIM-FRANKFORT  o.  M. 


No.  624.     May's  Watch  shaped  Speed  Counter 
with  measuring  wheel. 


The  great  advantage  ot  this  speed  counter,  other  than  its  extremely  convenient 
shape,  is  that  the  figure  dial  automatically  changes  to  correspond  with  the  direction  in 
which  the  shaft  is  rotating.  As  only  the  correct  set  of  figures  corresponding  to  the 
direction  of  rotation  can  be  seen  it  is  impossible  for  errors  in  reading  to  arise.  Two 
hands  similar  to  those  used  in  a  watch  show  the  number  of  revolutions  of  the  shaft. 
The  long  hand  marking  units  and  tens  and  the  small  hand  the  hundreds.  The  instru- 
ment is  easily  reset  by  opening  the  back  of  the  case  and  turning  a  small  milled  nut. 

The  triangular  point  can  be  quickly  replaced  by  a  small  disc  with  rubber  let  into 
the  circumference  and  exactly  20  cm  round,  to  measure  the  amount  of  cable  employed, 
belt  speeds  &c.,  the  readings  being  divided  by  5  to  give  the  result  in  metres. 

No.  624.    Speed  Counter  with  metre  measuring  wheel,   in   case. 

Price  M.  25.- 

The  first  wood  cut  shows  the  counter  after  use  against  a  shaft  revolving  in  the  same  direction  as  the  hands  of  a 
watch,  in  other  words,  to  the  right,  the  second  after  revolving  to  the  left;  the  reading  in  both  instances  being  738. 

A  milled  edged  nut  which  is  accessible  on  opening  the  back  of  the  case  enables  the  counter  to  be  easily  and  quickly 
reset  to  zero. 

No.  625.    The  same   Counter  with   Chronograph  (Second-watch). 

Price  on  application. 


134 


J 


^  HARTMANN  &  BRAUN,  BOCKENHEIM. FRANKFORT  o.  M.  ^ 

No.  627. 

Mechanical   apparatus  to  determine   the   sectional 
area  of  mains  or  the  fall  of  potential  therein. 

Helberger  system. 


This  apparatus  furnishes  wiremen  with  a  ready  means  of  ascertaining 
mechanically  the  correct  sizes  of  the  leads  in  electrical  installations, 
especially  the  requisite  sectional  area  of  the  mains  in  house  wiring  - 
the  sizes  for  branches  need  not  as  a  rule  be  determined  —  and  is  also 
very  useful  to  work  out  the  feeder  network  for  central  stations  in  fact 
for  all  installations  supplied  from  one  source. 

It  consists  of  a  two  armed  lever  in  which  the  long  arm  is  graduated 
and  the  short  arm  is  fitted  with  a  spring  balance  and  pointer. 

To  use  it,  weights  —  proportional  to  the  number  of  lamps  or 
amount  of  current  —  are  hung  on  the  graduated  arm  at  a  distance  from 
the  bearing  corresponding  to  the  actual  distance  of  the  lamps  from  the 
source  of  supply,  and  the  spring  is  then  screwed  up  until  the  lever  floats 
opposite  the  beam  pointer.  The  index  on  the  divided  circle  then  shows 
the  sectional  area  or  diameter  of  the  wire  practically  suitable,  allowing 
for  the  fall  of  potential  admissible,  the  latter  can  also  be  determined  for 
any  desired  sectional  area  without  further  manipulation. 

No.  627.     Apparatus  to  determine  the  sectional  area  of  mains, 

in  a  flat  wooden  case,  with  50  weights.  Price  M.  85. — 


185 


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HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


No.  628. 

Cable  Calculating  Apparatus.     Helberger  system. 

Patented. 

This  cable  calculating  apparatus  enables  the  sectional  area,  drop  in 
potential  and  distribution  of  current  in  a  network  of  mains  fed  at  various 
points  to  be  determined  in  the  most  simple  manner  without  any  compli- 
cated calculations. 

Experiments  proved  that  the  behaviour  of  a  thread  suspended  at 
two  points  and  loaded  with  weights  is  the  same  as  that  of  a  wire  to 
which  current  is  supplied  at  its  two  ends  and  from  which  current  is 
taken  at  several  intermediate  points,  and  this  fact  has  been  adopted  in 
designing  this  apparatus  for  calculating  cables. 

It  is  built  up  chiefly  of  several  cylindrical  graduated  rails  which  can 
be  connected  crosswise  together.  On  each  of  these  rails  two  moveable 
supports  are  mounted  which  carry  the  other  parts  necessary  to  adjust 
the  threads  and  read  off  the  results,  a  number  of  weights  and  an  arrangement 
to  determine  the  dip  of  the  thread  are  also  supplied.  These  parts 
correspond  to  the  factors  for  a  distribution  network  of  length  and  junctions 
of  the  mains,  loading  and  connections  thereto  and  also  for  the  fall  in 
potential  admissible. 

The  moveable  supports  are  arranged  on  the  rails  so  that  their  relative 
distances  apart  correspond  with  the  lengths  of  the  mains  between  the 
feeding  points,  they  are  then  connected  together  by  threads  on  which 
weights  proportional  to  the  number  of  lamps  or  current  supplied  are  hung 
at  distances  proportional  to  the  relative  distances  of  these  delivery  points. 
The  sliding  weight  on  the  lever  carried  by  the  support  is  now  adjusted 
until  the  dip  of  the  thread  corresponding  to  the  drop  in  potential  nowhere 
exceeds  a  given  amount. 

The  position  of  the  sliding  weight  then  affords  a  measure  for  the 
sectional  area  of  main  necessary  whilst  the  declination  angle  of  the  thread 
from  the  horizontal  indicates  the  distribution  of  the  total  energy. 

The  whole  apparatus  is  designed  to  render  all  manipulation  as  simple 
as  possible,  each  support  for  instance  being  fitted  with  a  thread  holder  in 
which  the  thread  is  automatically  wound  up  when  not  in  use.  The  decli- 
nation angle  of  thread  is  read  off  direct  on  a  small  scale  mounted  on  the 
lever  support.  The  dip  can  be  adjusted  for  various  losses  of  potential 
and,  like  the  weights,  is  calibrated  from  definite  mathematically  tested  units. 

The  apparatus,  owing  to  the  amount  of  tedious  calculations  obviated 
thereby,  is  especially  suited  for  use  in  a  engineer's  office,  and  also  for 
technical  schools  to  experimentally  demonstrate  the  application  of  Kirch- 
hoff's  law  to  calculations  for  central  stations. 

No.  628.  Cable  Calculating  Apparatus  with  one  longitudinal  and 
two  cross  rails  and  6  supports;  the  rails  made  of  brass  tube. 

Price  M.  600.— 

No.  628  a.    The  same  apparatus  with  the  rails  in  wood    „     510.  — 
Extra  cross  rails,  each  with  two  standards 

for  No.  628  M.  170.—  ;  for  No.  628a  M.  135.—. 

I  .  _ 

137 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o. 


Ring  insulators, 

protected  by  patents  and  registered  designs. 

A  new  system  for  wiring  inhabited  rooms  was  worked  out 
last  year  in  our  offices,  which  has  proved  very  successful  and  has 
to  a  very  great  extent  been  adopted  by  all  large  wiring  contractors. 

It  has  been  found  everywhere  where  central  stations  have  been 
erected  that  those  people  whose  houses  are  best  decorated  are  those 
whose  custom  it  is  most  difficult  to  obtain  and  therefore  the  central 
station  looses  or  rather  does  not  obtain  the  customers  who  would  con- 
sume the  largest  amount  of  current.  The  cause  for  this  is  to  be  sought 
in  the  fact  that,  if  the  wiring  is  carried  out  in  accordance  with  the 
rightly  somewhat  severe  rules  necessary  to  ensure  durable  work,  it 
offends  the  eye,  or,  if  concealed  behind  the  plastering,  the  making 
good  of  walls  and  ceilings  causes  in  any  case  great  mess  and  dis- 
turbance. 

The  ring  insulator  system  meets  the  requirements  or  the 
electrician,  the  architect  and  the  client  as  it  offers  every  advantage 
for  permanently  satisfactory  work,  can  be  matched  to  any  style  or 
tone  of  decoration  and  can  be  installed  without  causing  any  dirt  and 
at  a  considerably  less  cost  than  the  other  systems  usually  adopted. 

The  materials  necessary  for  installations  on 
this  system  are  made  in  two  sizes  and  a  large  stock 
of  same  is  kept  and  also  of  the  requisite  special  tools. 

All  packages  bear  the  trade  mark  illustrated 
at  side. 

Full  instructions  in  pamphlet  form  and  price 
lists  will  be  sent  on  application. 

The  chief  parts  of  this  ring  insulator  system  are  small  rings  or 
porcelain  or  glass  with  a  slot  round  the  edge  which  are  sprung  into 
brass  hooks  (plain,  nickelled,  or  stained  blue  or  brown). 

nal.Gr.. 

nahtfr. 


The  hooks  are  ornamented  with  embossed  rosettes  which  are 
either  suspended  on  round  headed  wood  screws,  a  method  chiefly 
adopted  in  hired  dwellings,  and  hospitals  or  for  temporary  purposes,  or 
else  are  nailed  up  using  always  small  wood  plugs  to  fasten  into  the  walls. 


138 


41 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 


Special  tools  are  pro- 
vided to  render  this  simple 
method  of  installation  as  easy 
as  possible.  Two  blows  with 
a  heavy  hammer  on  a  coni- 

cally    pointed    round    steel  ^  rnt  fr 

chisel  make  a  suitable  hole 
for  the  wood  plug  even  in  the  hardest  brickwork.  It  the  chisel  is  carefully  removed 
not  a  particle  of  dirt  or  dust  is  caused.  Another  hammer  blow  drives  the  dry  wood 
plug  into  the  hole  thus  made  using  no  plaster  whatever  except  in  the  case  of  extremely 
rotten  plaster  work.  Then,  using  the  seating  tool,  the  nail  hook  is  gently  hammered 
in,  the  rosette  hiding  the  wooden  plug. 


Screw  hooks  in  five  lengths  from  45  to  150  mm  are  provided  to  carry  leads 
from  the  wall  across  the  ceiling  to  a  chandelier. 

The  class  of  wires  most  suitable  are  flexible  cords  or  stranded  wires 
covered,  according  to  the  class  of  room  with  either  silk  or  worsted  to  match  the  colour 
of  the  paper  or  other  decorations.  Specially  shaped  wedges  of  insulating  material 
serve  to  clamp  the  wiring  in  the  insulator,  whilst  particular  forms  of  gripe  insulators 
are  provided  to  take  the  strain  of  the  wires  off  the  switch  or  cut-out  terminals. 

Split  rings  can  be  used  with  advantage  when  subsequently  inserting  new 
supports  or  using  very  heavy  long  leads. 

Improvements  in  all  the  other  work 
incidental  to  wiring  have  also  been  made, 
for  instance  the  flexibles  are  neatly  ended 
off  and  joints  made  without  the  dangerous 
use  of  solder  by  using  thin  metal  rings 
(eyelets),  the  bare  ends  of  the  wires  are  bent  into  these  rings  and  their  edges  are  closed 
over  and  flattened  by  suitable  pliers;  wires  finished  off  with  these  ends  are  connected 
together  sometimes  by  hollow  rivets  and  sometimes  by  a  special  type  of  screw  rivet. 

Special  wall  drills  and  attachments  are  also  made  enabling  the  thickest  walls 
to  be  pierced  without  noise  or  dirt  and  leaving  a  clean  cylindrical  hole. 

Using  these  ring  insulators  and  special  incandescent  lamp  holders  with  external 
contact  terminals,  gas  chandeliers  can  be  easily  and  neatly  converted  for  electric  light. 


139 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


XIII.    Telephones. 

No.  660a. 
Station  with  microphone  and  battery  call 


In  large  telephone  installations  or  in  smaller  ones  where  the  instruments  are  in 
constant  use  it  is  preferable  to  erect  instruments  which  although  dearer  than  the  usual 
class  of  telephones  are  however  of  far  better  workmanship  and  made  to  stand  hard 
work  without  damage,  of  this  class  more  than  80000  sets  have  been  supplied  to  and 
are  now  in  use  by  the  German  Post  Office  who  have  been  constant  customers  of  our 
firm  for  many  years. 

The  above  apparatus  with  carbon  pencil  microphones  in  which  the 
pencil  vibrations  are  controlled  by  springs  and  with  watch  shape  telephones 
of  our  own  design  are  supplied  for  use  either  with  battery  or  magneto 
calls.  The  cases  are  made  in  polished  walnut  wood  and  all  the  metal 
work  is  made  and  fitted  with  the  greatest  care  and  accuracy. 

No.  660.     Station  with  one  telephone  for  battery  call. 

No.  660 a.     As  above,  but  with  two  telephones. 

No.  662.     Station  with  one  telephone  and  magneto  call. 

No.  662a.     As  above,  but  with  two  telephones. 

Prices  of  these  instruments  which  are  not  supplied  singly,  but  only 
in  quantities  of  not  less  than  50,  will  be  quoted  upon  application. 

The  batteries  for  call  and  microphone  have  to  be  mounted  in  separate  cases  and 
are  not  supplied  with  the  instruments. 


140 


J 


HARTMANN  &  BRAUN,  BOCKENHEIM-  FRANKFORT  o.  M. 

' 


XIV.  Small  Dynamos  and  Motors. 


No.  638. 
Portable   Dynamo 

for 
blasting  purposes. 


This  portable  dynamo  is  specially  intended  lor  blasting  purposes  using  incandescent 
fuses  and  as  compared  with  the  use  of  static  electricity  has  the  advantage  that  it 
is  absolutely  independant  of  the  weather  and  that  failures  therefore  can  never  arise. 
It  is  however  suitable  for  all  purposes  where  a  current  at  a  high  potential  for  a  short 
space  of  time  is  required.  Special  attention  has  been  paid  to  designing  a  machine  as 
light  in  weight  as  possible  and  of  the  maximum  attainable  output.  The  weight  is 
approximately  10.8  Kilogrammes  and  at  3  revolutions  of  the  handle  per  second  the 
machine  gives  over  1  ampere  with  an  output  of  about  50  watts. 

No.  638.  Portable  Dynamos  with  switch  mounted  in  solid  oak  case, 
with  strong  leather  case  and  carrying  strap.  Price  M.  340. — 


Revolutions  per 
minute 

Potential 
in  volts 

Cu 
exte 

100 

rrent  in  a 
rnal  resis 

75 

mperes  in 
ance  of  c 

50 

an 
hms 

25 

Smallest  external 
resistance  admissible 
in  ohms 

2000 

19.5 

0.20 

0.26 

0.39 

0.78 

16 

*)  In  practice  the 
maximum  current 
admissible  is 
1.2  amperes. 

2500 

37.5 

0.38 

0.50 

0.75 

1.50") 

31 

2700 

42.0 

0.42 

0.56 

0.84 

1.68*) 

35 

Incandes 
ensure  firing. 


it  fuses  of  platint 


0.05mm  dia.  (a  lenght  of  about  5  mm  =5  ohms)  require  about  0.6  amper 


141 


^  HARTMANN  &  BRAUN,  BQCKENHEIM- FRANKFORT  o.  M.  Q 


No.  630.     Electromotors  for  direct  current. 


In  designing  the  larger  sizes  ot  electromotors  special  attention  is 
always  paid  to  attaining  the  highest  possible  ratio  of  efficiency  whilst 
this  point  has  been  mostly  disregarded  in  the  smaller  types.  In  these 
latter  the  efficiency  depends  chiefly  on  perfect  workmanship  in  the 
mechanical  details  and  their  manufacture  is  therefore  more  suited  to  a 
mechanician's  than  an  engineer's  workshop.  A  comparison  between  the 
efficiencies  mentioned  below  and  those  of  other  small  motors  will  justify 
this  statement. 

The  details  of  construction  in  the  motors  here  illustrated  have  several 
special  features,  the  fields  are  of  the  horse  shoe  type  with  ring  armature, 
they  are  absolutely  sparkless  even  if  overloaded  and  the  brushes  do  not 
require  adjustment,  the  commutator  is  of  hard  metal  and  in  conjunction 
with  the  round  carbon  brushes  affords  every  guarantee  for  continuous 
satisfactory  running  in  either  direction.  To  enable  the  motors  to  run  in 
any  position  grease  lubrication  is  adopted  for  the  bearings.  Like  all 
other  small  motors  these  are  wound  as  series  machines,  the  speed  there- 
fore varying  with  the  load. 

No.  630.    Electromotors. 


No.  630. 

Output 
H.  P. 

Watts 

absorbed 

Efficiency 
in'/o 

Revo- 
lutions 
per 

Diameters 
of  the  3  speed 
grooved  pulley 
in  mm 

SP 
Length 

ace  occup 
in  cm 

Breadth 

ed 
Height 

weight 
kg 

Price 
M 

Ill 

VM 

66 

55 

1700 

40,  50,  60 

20 

15 

18 

6,5 

165.— 

IV 

Yl5 

81 

60 

1700 

40,  50,  60 

20 

20 

21 

12,5 

170.- 

VI 
Res 

»/8 

istanc 

131 

98  to   I 

70 
egulate 

1500 

the  s; 

55,  80,  100 
jeed  special!} 

23 
T  quote 

28 
d  for. 

28 

30,0 

260.- 

142 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  632.     Electrically  driven  Ventilating  Fans. 


ca.Ven.  Gr. 


The  inconveniences  attached  to  working  ventilating  fans  in  houses  and  especially 
in  workshops,  due  especially  to  the  high  speed  at  which  they  require  to  run,  to  a  great 
extent  prevent  their  use.  This  latter  point  however  is  one  specially  adapted  to  be  dealt 
with  by  electrical  means  where  available,  and  where  fresh  air  or  the  removal  of  hot 
air  or  noxious  fumes  is  required.  Electromotors  owing  to  the  small  space  they  occupy, 
easy  starting  and  slight  attention  required  are  extremely  suitable  for  driving  these  fans 
Both  motor  and  fan  are  mounted  together  on  a  cast  iron  bracket  and  the  iron  tube 
which  is  built  into  the  wall  is  concealed  by  a  moulded  frame.  All  parts  are  highly 
lacquered. 

No.  632.     Electrically  driven  Ventilating  Fans. 


No.  632. 


Ill 


IV 


VI 


Watts  absorbed  .     .     . 

66 

81 

131 

Diameter  of  fan  .     .     . 

250 

300 

350 

Price  in  M.      ... 
Resistances  to  regulate 

210.- 

the  speed 

215.— 

specially  qi 

320.— 

toted  for. 

143 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 

' 


XV.    Electrical  Thermometric  Apparatus. 

Prof.  Braun's  Standard  Pyrometer. 

The  Braun  Pyrometer  for  measuring  high  temperatures  up  to  1200°  Celsius, 
is  based  on  the  alteration  in  resistance  of  a  platinum  wire  in  accordance  with  the 
temperature  of  the  chamber  in  which  it  is  inserted.  This  platinum  wire  which  is  wound 
non-inductively  on  a  fire  clay  former  and  mounted  in  a  fire  proof  tube  forms  one  arm 
of  a  Wheatstone  bridge  in  connection  with  a  sensitive  galvanometer  by  means  of  which 
the  existing  resistance  can  be  easily  ascertained  or  in  other  words  temperature  read 
off  direct  in  degrees. 

The  actual  measuring  apparatus  is  fitted  into  a  strong  lock  up  oak  case  and  so 
arranged  that  only  those  parts  requiring  adjustment  are  accessible,  the  cells  are  mounted 
in  a  separate  compartment  closed  by  a  cover  at  the  back  of  the  case,  the  galvanometer 
is  also  fitted  into  a  separate  case  for  travelling  purposes,  can  be  used  in  any  position 
and  is  unaffected  by  external  magnetic  fields. 

The  working  of  the  apparatus  is  extremely  simple  and  can  be  carried  out  by 
any  unskilled  person. 

The  instrument  is  suflficientlv  sensitive  to  render  an  increase  or  decrease  of  a 
few  degrees  of  heat,  even  at  the  highest  temperatures,  distinctly  perceptible.  The 
degree  of  absolute  accuracy  is  extremely  high  as  the  instruments  are  calibrated  in 
connection  with  a  great  number  of  readings  taken  with  the  porcelain  air  thermometer. 

The  pyrometers  are  supplied  graduated  to  either  1000  or  1200°  Celsius  the 
measuring  apparatus  in  both  patterns  is  the  same  but  the  construction  of  the  pyrometer 
is  essentially  different. 

No.  480  a.  Pyrometer  bridge  with  a  galvanometer  easily  set  up 
for  use  in  any  position,  calibrated  as  desired  to  either  1000  or  1200°. 

Price  M.  425.- 

No.  482.  Pyrometer  in  iron  tube  fitted  with  pure  nickel  cover, 
and  protected  by  an  iron  sheath  lined  internally  with  thin  platinum 
sheet,  suitable  for  temperatures  up  to  1000°. 

Price,  exclusive  of  the  platinum  lining  M.  240.  — 
The  platinum   lining,   weighing  about  75   grammes,   is  charged 
extra  according  to  the  market  price  of  platinum. 

No.  482  a.  Pyrometer  in  iron  tube  fitted  with  pure  nickel  cover, 
covered  at  the  base  by  a  thick  platinum  sheath  specially  protected 
against  external  damage,  suitable  for  temperatures  up  to  1200°. 

Price  exclusive  of  the  platinum  lining  M.  240.  — 

The  platinum  lining,  weighing  about  200  grammes,  is  charged 
extra  according  to  the  market  price  of  platinum. 

Soft  flexible  wire,  about  3  sq.  mm.  area,  for  a  distance  of  10  metres, 
with  solid  ends.  Price  M.  10.  — 

Instructions  for  use:  After  inserting  the  Pyrometer  into  the  chamber  of  which  the  heat  is  to  be  tested  until 
the  lower  flange  of  the  instrument  projects  therein,  its  terminals  are  connected  by  stout  wires  or  cable  to  the  two  large 
terminals  on  the  left  side  of  the  apparatus,  the  galvanometer  being  connected  by  thinner  wires  to  two  smaller  terminals 
on  the  right  hand  side  of  the  apparatus. 

To  take  a  reading  the  lever  projecting  at  the  side  is  drawn  forward  to  connect  the  battery  and  galvanometer,  and 
the  disc  adjusted  until  the  galvanometer  is  not  deflected.  The  marks  engraved  on  the  scale  then  give  without  any  reckoning 
the  temperature  of  the  pyrometer  in  degrees  Celsius,  a  special  feature  of  this  pyrometer  as  compared  with  other  similar 
instruments.  The  entire  adjustments  can  be  made  without  opening  the  case. 

The  distance  between  the  pyrometer  and  the  measuring  apparatus  can  be  any  desired  amount,  the  use  of  the 
instrument  as  a  Telepyrometer  offering  no  great  difficulty.  Data  for  the  necessary  sectional  area  of  the  cables  or 
leads  for  measurements  at  a  distance  will  be  furnished  on  receipt  of  particulars  showing  the  proposed  distances. 


144 


r 


145 


rr~ 

HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o. 


Telethermometer. 

The  Telethermometer  is  an  apparatus  easily  used  by  unskilled  hands  to  deter- 
mine the  temperature  in  distant  rooms  such  as  class  rooms  or  offices  which  are  all 
heated  from  one  source,  in  greenhouses  or  inaccessible  rooms  such  as  malting  floors, 
drying  ovens,  especially  in  pottery  works,  in  enamelling  ovens  &c.  The  measurements 
can  be  made  either  in  the  stoke  hole,  or,  if  it  is  to  be  used  as  a  check  on  the  attendant, 
without  leaving  the  office.  Like  the  Braun  Pyrometer  it  depends  on  the  electrical 
resistance  of  a  metal  varying  in  accordance  with  the  temperature. 

Thermometer  No.  485  consists  of  a  bifilar  winding  on  a  very  slender  insulated 
polygonal  mould  which  is  protected  by  a  perforated  iron  case,  this  form  responds 
quickly  to  the  slightest  variation  of  temperature  and  can  be  used  wherever  the  atmosphere 
is  not  too  damp  or  contains  too  much  acid  fumes.  In  the  latter  case  and  for  use  in 
liquids  such  as  in  a  mash  tub,  the  thermometers  No.  486  which  are  hermetically  sealed 
in  metal  cases  are  preferable. 

The  Indicator  or  measuring  apparatus  for  the  telether  mo  meter  is 
mounted,  together  with  a  sensitive  galvanometer  which  is  uninfluenced  by  the  magnetic 
meridian  or  by  external  iron,  in  an  oak  case  to  fix  against  the  wall,  and  the 
temperature  scale  engraved  on  the  circular  dial  is  protected  by  a  glass  front.  The 
measuring  battery  is  contained  in  a  separate  case  which  can  be  placed  wherever  most 
convenient.  The  thermometer  and  measuring  apparatus  are  connected  together  by  well 
insulated  wires  fixed  side  by  side. 

Only  one  measuring  apparatus  is  necessary  to  read  oft'  the  temperature  existing 
in  several  places  as  the  measuring  wire  of  each  thermometer  can  be  made  to  correspond 
in  several  instruments,  in  this  case  a  separate  lead  is  taken  from  each  thermometer 
to  the  measuring  apparatus  whilst  all  can  be  connected  to  a  common  return  wire. 

The  apparatus  is  supplied  to  measure  temperatures  from  20°  below  to  300°  above 
zero  in  the  following  patterns. 

No.  484.  Telethermometer  with  25  contacts,  to  measure  25  single 
degrees  or 

50  degrees  reading  from  2  to  2  degrees  (e.  g.  from  30  to  80)  or 
125          „  „  „      5    „    5 

including  battery  in  separate  case.  Price  M.  285. — 

No.  484a.    Telethermometer  with  50  contacts,  to  measure 
50  single  degrees  (e.  g.  from  —20  to  +30°)  or 
100  degrees  reading  from  2  to  2  degrees 
including  battery  in  separate  case Price  M.  340. — 

No.  485.  Thermometer  in  perforated  case  for  temperatures  up  to 
150  degrees each  M.  25. — 

No.  486.  Thermometer  in  closed  case  for  temperatures  up  to 
150  degrees each  M.  30.— 

No.  486a.    Thermometers  for  temperatures  up  to  300  degrees 

each  M.  36. — 

Plug  or  lever  Commutator  switch  for  2,  3,  4,  5  &c.  to  12  ther- 
mometers. 

Price  M.  10.—,  15.-,  20.-,  25.—  &c.,  to  M.  60.— 

Instructions  for  use.  The  removeable  key  **?  is  inserted  into  the  hole  in 
the  centre  of  the  disc  and  the  pointer  Z,  slowly  turned  over  the  circle  of  metal  contacts 
until  the  galvanometer  needle  G  is  brought  back  to  its  zero  position,  the  temperature 
is  then  read  off  opposite  the  pointer  Z  direct  in  degrees  Celsius.  When  the  measure- 
ment is  completed  the  withdrawal  of  key  S  breaks  the  circuit. 

I  J 

146 


Telethermometer-Installation. 


":  I 

il 

ii  Ik 

The  engra 

ng  shown  an  appi- 

1 

ratus  with  50 

ontacts,  suitable  for 

ii  !l 

temperatures  fr 

m  20  to  120  degrees, 

".!'\ 

reading  each    2 

degrees   with   three 

!ll!l 

thermometers,  i 

has  therefore  a  plug 

:).  :•   ,  • 

switch  for  the 

hree  lines. 

'"fllf  }1 

/ii        ;!    ! 

The  leads 

re  of  well  insulated 

Jlllllll 

wire  1.5  to  2 

m  sectional  area   of 

copper  and   an 

large  variations  in 

llli 

length  of  the  v 
sed  bv  inserting 

dditional  rpsist;im-p«; 

11 

between  the  terminals  and  the  plug 
switch. 


No.  484  a. 

Size  of  case: 
63x35x15  cm. 


'Ill 


147 


^  HA&TMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  ^ 

rso  •KSjp' C/1 

XVI. 

Collection  of  simple  electrical  instruments 
for  Schools. 

We  have  been  led  to  design  this  collection  of  cheap  electrical  measuring  instru- 
ments by  the  many  enquiries  we  have  received  for  the  simplest  class  of  apparatus 
of  mechanically  perfect  construction,  to  demonstrate  experimentally  Ohm's  law  which, 
we  are  pleased  to  say,  has  latterly  received  attention  in  the  science  classes  of  schools; 
thereby  inculcating  at  an  early  period  a  knowledge  of  the  electrical  units,  which  from 
the  many  commercial  uses  to  which  electricity  is  now  applied,  is  of  great  advantage. 

Many  of  the  instruments  employed  in  teaching  Physics  and  especially  in  teaching 
Electricity  are  designed  on  a  principle  which  the  pupil  cannot  understand  and  which 


No.  580. 
School- 


Galvano- 
meter. 


Vi  n.  Gr. 


in  some  instances  is  not  clear  to  the  master,  with  the  idea  we  presume,  of  rendering 
them  extremely  sensitive  or  universally  applicable;  very  often  too  they  are  made  in  such 
small  sizes  that  their  method  of  working  cannot  be  seen  by  scholars  sitting  some  distance 
off  or  even  to  render  it  possible  for  them  to  note  the  position  of  the  index  pointer, 
frequently  too  the  instruments  are  elaborately  got  up  and  such  unsuitable  colours  em- 
ployed, that  it  is  extremely  difficult  for  an  onlooker  to  recognise  the  actual  working  parts. 

In  the  following  collection  we  have  attempted  to  meet  the  want  of  instruments 
free  from  the  above  defects.  Every  instrument  is  constructed  in  the  simplest  possible 
manner  and  arranged  that  every  working  part  can  be  seen  from  a  distance  and 
especially  that  the  scales  are  very  clear  and  easily  read.  At  the  same  time  the  instru- 
ments can  be  used  with  a  comparatively  great  degree  of  accuracy  and  are  therefore 
available  for  the  teachers  own  private  use,  for  which  purpose  some  of  them  are  fitted 
with  additional  finely  divided  scales. 

The  wood  work  is  of  dull  polished  mahogany  and  the  metal  parts  are  simple  in 
design  but  accurately  made.  No  levelling  screws  are  provided,  as  the  instruments  will 
work  on  any  somewhat  unlevel  table  without  adjustment,  wood  wedges  are  however 
sent  with  them  so  that  they  can  be  levelled  by  the  Quincke  method  if  desired. 

The  designs  of  most  of  these  instruments  are  registered. 


148 


HARTMANN  &  BRAUN,  BOCKENHEIM- 


n.  Gr 


No.  580.    School  Galvanometer. 

The  School  Galvanometer  is  so  constructed  that  it  can  be  entirely  dismounted, 
that  it  can  be  entirely  taken  apart  and,  whilst  explaining  the  action  of  every  part,  be 
put  together  in  front  ot  the  scholars  somewhat  after  the  following  manner: 

One  of  the  magnets*) 
is  pushed  into  the  lower 
carriage  on  the  suspension: 
Compass  or  Magneto- 
meter. 

One  coil  is  placed  paral- 
lel to  the  magnet :  simple 
Galvanometer.  The 
other  coil  is  similarly  ad- 
justed and  the  windings 
coupled  in  series  or  pa- 
rallel, finally  the  two  coils 
are  moved  symetrically 
to  the  magnet:  Varying 
degrees  of  sensitive- 
ness. 

The  copper  sheath  is 
inserted  inside  the  coils: 
Vibrations  damped. 

The  windings  of  the 
two  coils  are  connected 
in  opposite  directions: 
Differential  Galvano- 
meter. 

The  other  magnet  is  in- 
serted in  its  carriage :  As-  i 
tatic  Galvanometer. 

The    pointer    is    adjus- 
table as  regards  the  mag- 
net it  can  therefore  always 
be  arranged   to  point  to- 
wards  the  scholars  after 
the     coil    windings    have 
been    placed    parallel    to  J 
the  pole  axis  of  the  mag-  Q 
net    or    in    the    magnetic 
meridian. 

No.  580.  School  Galvanometer  with  scale  graduated  in  divisions  ot  5  degrees 
for  the  scholars  and  a  second  scale  graduated  in  single  degrees  for  the  teacher's  use; 
sensitiveness  with  one  magnet,  therefore  not  astatic,  with  the  coil  windings  in  series 
1  degree  deflection  =  0.00004  ampere.  Price  M.  75.— 

No.  580  a.  Tangent  galvanometer  ring  in  copper  mounted  on  wood  tripod 
stand,  the  galvanometer  base  fitting  centrally  on  the  top  of  stand.  Price  M.  30.— 

When  set  up  as  Tangent  galvanometer  the  instrument  is  suitable  for  measuring 
currents  up  to  15  amperes  (10  amperes  =  60°  deflection),  to  enable  the  teacher  to  make 
more  accurate  measurements  the  large  pointer  can  be  replaced  by  a  smaller  one  to 
read  on  the  more  finely  divided  scale. 


*)  The  magnets 
iible  as  possible. 


ade  of  thin  steel  tube,   both   to   reduce  the  moment  of  inertia  and  to  render  them  as 


149 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  581.    Measuring  wire  for  resistance  bridge. 

A  measuring  wire  of  constantan,  1  metre  long  is  stretched  between  two  double 
terminals  over  a  scale  divided  into  millimetres.  The  side  of  the  base  faceing  the 
scholars  is  divided  by  wide  black  lines  on  a  white  ground  into  spaces  of  o  centimetres 
with  the  central  4  decimetres  into  single  centimetres.*) 


No.  581.  Measuring  wire  for  resistance  bridge;  Range,  using 
the  galvanometer  described  overleaf  and  the  resistances  illustrated  below 
0.01  to  100  ohms.  Price  M.  30.— 


One  terminal  at  both  the  right 


eft  hand  ends  of  the 


(1—3  cells);  one  terminal  of  the  comparative  resistance  is  connected  to  an  end  of  the  resistance  to  be  tested   and  the  t 
remaining  tree  ends  are  connected  to  the  other  terminals  of  the  measuring  wire,  the  galvanometer    being  con 


f  a  battery 
nd  the 
ted  bet 


the  junction  of  the  unknov 


sliding  contact. 


No.  582.    Comparative  resistances  for  school  work. 

These  comparative  resistances  are  made  with  non  inductive,  free  stretched  wires. 
The  smallest  resistance  of  0.1  ohm  is  made  of  8  rows  of  copper  wire,  the  1  ohm 
resistance  is  in  one  row  of  German  silver  and  the  10  ohm  resistance  is  in  ten  rows  of 
the  same  material,  all  the  wires  are  of  the  same  diameter  so  that  the  varying  con- 
ductivity and  the  ratio  between  length  and  resistance  can  be  clearly  demonstrated. 


No.  582.    Three  comparative  resistances  of  0.1,  1  and  10  ohms.**) 

Price  M.  25.- 


")  Not  shown  in  illustration. 

*)  The  resistance  of  10  ohms  is  now  divided  in  two  parts  and  fitted  with  a.  branch  terminal  for  2x5  ohms. 


150 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M. 


No.  583.    School  Voltmeter. 


The  principle  of  the  Kohlrausch 
spring  galvanometer  must  certainly  be 
considered  the  simplest  design  on  which 
to  base  the  construction  of  a  -direct  reading 
galvanometer.  An  iron  core  is  sucked  into 
a  solenoid ;  the  tension  it  exerts  on  a  spiral 
spring  supporting  same  acts  as  counter- 
force;  the  distance  it  is  drawn  into  the 
solenoid  is  a  measure  of  the  pressure  at  the 
terminals,  relatively  of  the  current  passing 
through  the  solenoid.  To  magnify  this 
small  movement  for  demonstration  pur- 
poses, both  the  iron  core  and  the  spring 
are  mounted  on  a  lever  which  is  connected 
to  a  moveable  arbor  and  pointer. 

No.  583.     School  Voltmeter, 

with  a  range  of  0.5  to  3  volts,  suit- 
able therefore  to  measure  the  E.  M.  F. 
of  single  galvanic  cells  elements,  with 
extra  resistance  to  increase  the  range 
to  30  volts.  Price  M.  40.- 


No.  584.    School  Ammeter. 


The  construction  of  this  ammeter 
is  similar  to  that  of  the  voltmeter,  the 
principal  difference  being  in  the  winding 
of  the  solenoid  and  the  calibration.  In 
both  instruments  the  current  is  brought 
to  the  terminal  at  the  left  hand  side 
and  to  the  terminal  in  the  middle  01 
the  base.  Whilst  the  sensitiveness  of 
the  voltmeter  is  varied,  or  the  range 
extended,  by  removing  the  coupling 
piece  between  the  middle  and  the  right 
hand  terminal,  in  the  ammeter  the  shunt 
is  connected  by  inserting  the  coupling 
piece  between  them.  If  the  approximate 
pressure  or  intensity  is  not  previously 
known  the  measurements  should  always 
be  commenced  with  the  least  sensitive 
arrangement  of  the  instrument,  in  other 
words  with  the  series-  or  shunt-resistance  Lni 
in  circuit. 

No.  584.   School  Ammeter 
with  a  range  of  0.2  to  2  amperes, 

which  by  means  of  a  shunt  of  one  fourth  of  the  resistance  of  the  solenoid 
can  be  extended  to  10  amperes.  Price  M.  40.  — 

Millboard  covers  are  supplied  with  both  these  instruments. 


151 


r 


HARTMANN  &  BRAUN,  BOCKENHEIM- FRANKFORT  o.  M.  c 


No.  585.    Induction  Apparatus. 

The  coils  in  this  instrument  are  very  carefully  insulated;  the  secondary  coil  is 
moveable.  A  condenser  which  can  be  switched  in  and  out  of  circuit  is  fitted  in  the 
base.  The  instrument  is  applicable  to  a  great  many  purposes.  Using  current  supplied 
from  a  few  cells  it  is  well  adapted  to  generate  alternating  currents,  such  as  are  required 
when  using  a  telephone  to  measure  the  resistances  of  electrolytes,  it  vividly  incandesces 


Geissler  tubes  and  answers  the  purpose  ot  a  transformer  to  demonstrate  the  conversion 
of  a  low  into  a  high  pressure  current  using  small  incandescent  lamps;  finally  it  can 
be  used  in  combination  with  the  school  galvanometer  for  the  Faraday  experiments  in 
induction,  for  which  purpose  a  bar  magnet  is  supplied  to  replace  the  iron  core. 


No.  585.    Induction  coil  with  condenser. 

on  the  two  coils  about  1  :  10. 


Ratio   of  the  winding 
Price  M.  80.— 


No.  586.    Telephone  for  demonstration  purposes. 


This  telephone  comprises  all  the  essential  parts,  magnet,  induction  coil  and 
diaphragm  all  visibly  arranged  and  easily  taken  apart.  It  can  be  used  as  an  alternating 
current  instrument  for  measuring  the  resistances  of  liquids,  for  which  purpose  a  galvano- 
meter is  not  per  se  a  suitable  instrument. 

The  method  of  connecting  the  unknown  and  the  comparative  resistances  to  the 
bridge  remain  the  same,  but  the  secondary  coil  terminals  of  the  induction  apparatus 
are  connected  to  the  bridge  terminals  instead  of  the  battery. 

No.  586.    Telephone  for  demonstration  purposes.    Price  M.  15.— 


152 


r1" 


INDEX. 


NOS. 

348  &  348  a 

349  &  349a 

350  —  354  . 
355—357  . 
358  &  359 


361  &  361  a 

362  &  362  a 

363  ... 

364  &  365 

366  I  &  II 

367  ... 

367  a     .     . 

368  ... 

369  ... 


Page 

Stands  for  Reading  Telescopes    .........    .....  5 

Gauss  Stands    .....................  5 

Reading  Telescopes,  not  mounted    .............  5 

„  fully  mounted  ............  2 

„                  „             simply  mounted  ............  4 

Scales  on  wood  and  celluloid  ...............  6 

„        „    plate  glass  and  opal  glass    ............  6 

Lanterns  for  scale  reading  ................  6 

Mirror  Distance  Indicator     ................  6 

Vertical  Detector  and  Vertical  astatic  Galvanometer  ......  124 


Simple  dead-beat  Galvanometers  with  pointer      ........  7 

Dead-beat  Differential-Galvanometer     ............  8 

Portable  dead-beat  Galvanometer  with  Telescope     .......  9 

Kohlrausch  Mirror  Galvanometer      .............  16 

Rosenthal  Micro-Galvanometer     ..............  17 

370,  370  a  &  370  b.     Astatic  Mirror  Galvanometers  (ballistic)    ........    17—19 

371  &  371  a.     Dead-beat  Reflecting  Galvanometers  with  bell  magnet     ....    10—12 

372  &  372  a   .     Astatic  dead-beat  Galvanometers      ............    20—21 

373  ....     Lecture-Room  Galvanometer    ............     ...  13 

374  &  374a   .     Tangent  Galvanometer  for  absolute  measurements  .......  24 

375  ....     Simple  Compass       ...     ................  24 

376  &  376  a   .     Tangent  Galvanometer  for  technical  use       ..........  25 

378  ....     Unifilar-Electrodynamometer  for  small  currents    ........  22 

379  I—  X  &  379  a  I-IV.     Spring  Galvanometer,  Kohlrausch  type    .......  100 

879  b  I—  IV   .     Electromagnetic  Ammeters  for  direct  current,  small  size,  round  shape  102 

379  c  I-XI   .                   „                     „           „        „          „         larger  size,     „          „  102 

379d  I—  IV   .     Electromagn.  Ammeters  for  alternat.  currents,  small  size,      „           „  102 

379  e  I—  XI  .               „                   „            „          „                „      larger  size,     „          „  102 

380  &  380  a  I  -VIII.     Small  Spring  Galvanometer,  on  wall  and  on  foot  .....  101 

381  I-  VII     .     Portable  Voltmeter       ..................  104 

381  M    .     .     .     Inspector's  Voltmeter  in  travelling  case  ...........  104 

381  a  D  &  381  a  W.     Marine  Voltmeter  with  ceiling  plate,  or  with  bracket  ....  104 

381  b  I  —  XII  .     Electromagnetic  Voltmeter  for  direct  current,  small  size,  round  shape  103 

381  c  I  -XII.                  „                       „            „       „            „        larger  size,      „           „  103 

381  d  I—  XII.     Electromagn.  Voltmeter  for  alternat.  currents,  small  size,      „           „  103 

381  el-  XII.              „                     „            „         „                „        larger  size,      „           „  103 

382  &  382  a  I-IV.     Simple  Voltmeters  for  galvanoplastic  work      .......  105 

383  &  383a  .     Universal  -Voltmeters,  largest  sizes  for  Central  stations   .     .     .     106—107 

384  a,  b  &  c   .     Insulation  Testers  for  Wiremen  ..............  133 

385,  385  a  &  385  b.     Water-,  Silver-  and  Copper  -Voltameters  .........  26 

387  ....     Opal  Glass  Photometer    .................  87 

388  ....     Portable  set  for  Resistance  measurements  ..........  61 

389  ....     Wheatstone-Kirchhoff  Bridge,  Kohlrausch  Roller  type     .....  36 

389  a      ...              „                  „                „         with  stretched  wire  .......  36 

390  ....     Induction-Apparatus,  Kohlrausch  type  ............  36 

391  &  391  a   .     Kohlrausch's  Universal  Bridge  and  Simple  Bridge  ......    60-61 

392  &  392  a   .     Vessels  with  platinum  electrodes,  Kohlrausch  and  Arrhenius  types  36 


153 


NOS.  Page 

393  I— VII     .     Standard  Resistance  Boxes  in  Series  of  6  resistances 41 

393  a  I -VII  .  „                  „                „       in  Decades  of  10  resistances     ....  42 

393b  I-VII  .  „                  „                „                  ,,          ,,6           „             ....  42 

393  c  I  ...  „                  „                 „       for  large  currents  with  Mercury  contacts  43 

393d  II— VI  .     Resistances  for  ordinary  testing  with  Plug  contacts 44 

393  e  II— VI  .     Decade  Rheostats  with  Switch  contacts 45 

394—402  .     .     Standard  Series  Rheostats  with  tenths 41 

394a— 402a  .            „               „               „          without  tenths 41 

394d-402d.     Series  Rheostats  for  ordinary  testing,  Plugs 44 

394  e— 402  e  .     Decade  Rheostats  for  ordinary  testing,  Switches 45 

4O3,  403 a- c  .    Standard  Branch  Rheostats 42 

403d&403e.  Simple  Branch  Rheostats  with  Plug-,  and  Switch-contacts    .    .     .   44—45 

404,  404  a  &  404  b.     Shunt  Rheostats  with  2,  3  or  4  resistances       .......  43 

405  ....     Standard  Bridge  up  to  approx.  110,000  ohms 46 

405d&405e.     Ordinary  Bridges  with  Plug-,  and  with  Switch-contacts 47 

407   ....     Standard  Bridge  up  to  11  million  ohms 46 

407  d  &  407  e.     Ordinary  Bridges  with  Plug-,  and  with  Switch  contac 47 

408,  408  a  &  b.     Additional  Rheostats  with  2,  3  or  4  resistances 43 

409d  I— VII  .     Single  resistances 44 

410  ....  Portable  Bifilar- Variometer  for  terrestrial  magnetism,  Kohlrausch  type  68 

411  .     .     .     .  Intensity- Variometer  for  terrestrial  magnetism,  Kohlrausch  type       .  71 
41  la     .     .     .     Simple  Local- Variometer,  Kohlrausch  type 71 

412  ....     Absolute  Bifilar-Magnetometer,  Kohlrausch  type       72 

413  ....    Absolute  Bifilar-Galvanometer,            „              „           72 

415  &  415  a  .    Unifilar  Magnetometers,                       „              „          72 

420  ....  Compensation  Magnetometer,  Weber  &  Kohlrausch  type     ....  72 

421  ....     Gauss- Weber  Magnetometer 72 

425  &  425  a  .    Earth-Inductors,  W.  Weber  type 74 

426  ....     Differential  Earth  Inductor,  L.  Weber  type 75 

427  ....    Astatic  Reflecting  Galvanometer 19  &  74 

431  ....    Large  Electromagnets       76 

446  ....    Spectrometer 85 

450  ....    Nippoldt's  Telephone  Bridge 58 

451  ....    Simple  pocket  Galvanometer  with  index  pointer 58 

452  ....     Complete  lightning  conductor  Testing  set 59 

454  &  454  a  .    Kohlrausch  Total  Reflectometers 85 

456  ....    Small  Spherometer       86 

460  &  460  a  .    Small  Milliamperemeters  for  medical  use 105 

461  ....    Large  Milliamperemeter     „           „           „ 105 

461  a     .    .    .    Large  Standard  medical  Milliamperemeter 97 

466  ....    Small  Cathetometer 86 

477  ....    Small  Theodolite 86 

480a     .    .    .    Pyrometer  Bridge , 144 

482&482a  .    Electrical  Pyrometers 144 

484&484a  .    Telethermometers 146 

485,  486  &  486  a.    Electrical  Thermometers 146 

490  &  490  a  .     Simple  and  double  Key,  du  Bois-Reymund  type 62 

491,  491  a  £  491  b.   Simple,  double,  and  double  successive  Keys  with  platinum  contacts  62 

492, 492  a  &  492  b.        „  „          „          „              „             „       „      mercury  cups      .  62 

493,  493  a  &  493  b.    Commutators  with  plug,  brush,  and  spring  contacts      ....  62 

494  &  494  a   .     Revolving  Commutator  and  rocking  Commutator 63 

495  &  495a  .    New  Switch  and  Weber  Switch 63 

496  ....    Daurer's  Universal-Pachytrop,  Battery  Selector 63 

J 


154 


NOS.  Page 

497  &  497  a   .  Charge  and  discharge  Keys  on  Sabine's  principle 64 

498  ....  Compensation-Key,  Lord  Kelvin's  method 65 

499  &  499 a   .  Spring  Commutators  and  Switch  for  insulation  testing 65 

5O1.  a  &  501  c  .  Dry  Cells  for  measuring  purposes 66 

502  ....  Portable  Battery  of  dry  cells  coupled  in  series  in  case 67 

503  ....  Hydrometer  for  Accumulators 108 

504  ....  Bismuth  Spiral  for  measurements  of  magnetic  fields 77 

505  ....  Magnetic  field  explorer 108 

506  ....  Portable  Universal  resistance  measuring  apparatus 48 

507  ....  Cable  Testing  cart  and  tent 56 

508  ....  Bridge  for  low  resistances 50 

508  a     .     .     .  Lord  Kelvin's  Double-Bridge 51 

509,  509 a  &  509 b.     Portable  Apparatus  for  measuring  insulation  resistances.     .    53—54 

510  &  510a  I — IV  Contact  voltmeters  for  direct  and  alternating  currents    ....  110 

511,  511a  &511b.     Single  and  compound  relays Ill 

512  I — III .     .  Signal  apparatus  with  optical  and  sound  alarms 112 

513  ....  Alarm  Voltmeter 113 

514  ....  Differential  Voltmeter  with  alarm 115 

515  ....  Vertical  Detector  (German  Post  Office  type) 124 

516  ....  Horizontal  Detector  (Swiss  Post  Office  type) 124 

520  ....  Commutator  to  switch  in  series  or  parallel 128 

521  &521a  III— V    Automatic  Switch  for  maximum  and  for  minimum  current   .     .  129 

522  ....  Current  Index 101 

523  ....  Simple  cell  switches 130 

524  ....  Instantaneous  cell  switches 130 

525  ....  Automatic  battery  switches 131 

526  ....            „           shunt  regulators 131 

526  a     ...            „            main  current  regulators 131 

527  I— VIII    .            „           double  switches  for  direct  current 123 

527  a  I-VIII            „                „              „          „     alternating  current 123 

530  ....  Direct  reading  Galvanometer  to  read  in  volts  and  amps 28 

530a     .     .    .         „            „                   „               „       „      „    amps,  only    .......  28 

530b     .     .     .                       „                    „                „       „      „    volts  only 28 

531  ....         „            „        Electrodynamometer  for  large  currents 29 

532  .     .     .     .         „             „                        „                       for  small  currents 29 

533  ....         „            „     .    Wattmeter .  29 

534  ....  Accumulator  cell  tester  (Pocket  voltmeter) 108 

535  &  535  a  .  Suspended  moveable  coil  Galvanometer  with  pointer  and  mirror    .  15 

536  &  536  a  .  Simple  moveable  coil  Galvanometer 15 

537  II— X  .     .  Recording  Ammeters  for  direct  current 120 

537  a  II— X    .            „                    „           for  alternating  current 120 

538  II — X  .     .  Recording  Voltmeters  for  direct  current 120 

538  a  II— X    .            „                    „          for  alternating  current    .........  120 

540  I-VIII    .  Watthour  meter  for  direct  current 121 

541  a  I— VIII.            „              „       for  alternating  current 121 

543  I— II  .     .  Electrodynamic  spring  balance  (Wattmeter) 119 

544  ....  Electrical  Time  meter  for  direct  current 122 

544  a      ...            „              „           „       for  alternating  current 122 

551  ....  Standard  Clark  cell,  Physico -Technical  Institution  model 30 

552  I— VII     .            „         Resistances  from  0.1,  1,  10  up  to  100000  ohms  ^    Physico-    (  ^ 

553  ....            „                  „            of  0,01  ohm  as  branch  resistance  >  Technical  <  30 

554  ....            „                  „            of  0,001  ohm   „         „                „         Jlnst.modeU  31 

555  ....  Petroleum  baths  for  standard  resistances 31 


155 


Nos.  Pugc 

556  ....     Large  Compensation  Apparatus  I  for  exact  current  and  potential  mea-  f  33 

557  .     .    '.-  '.-.Simple  Compensation  Apparatus]  surements,Phys.-Techn.Inst.  models]  35 
560  ....     Simple  apparatus  for  investigating  the  magnetic  properties  of  iron  78 
500 a     .   M»  .:   Complete;.',,      ,      „     .          „               „             „                  „             ,,       „  79 

570  ....     Standard  Photometer  with  rails  &  accessories,  Lummer-Brodhun  type  88 

571  .     .     .     .     Photometer- of  a  simpler  construction 88 

577   ....     Simple  Incandescent  lamp  Photometer  on  the  Joly  principle   ...  90 

580  ....    School-Galvanometer 148 

580  a     .     .     .     Tangent  galvanometer  ring  for  school  galvanometer 149 

581  ....    Measuring  wire  for  resistance  bridge 150 

582  ....    Comparative  Resistances  for  school  work 150 

583  ....    School  Voltmeter 151 

584  ....    School  Ammeter 151 

585  ....    Induction  Apparatus 152 

586  ....     Telephone  for  demonstration  purposes 152 

594  ....     Electrostatic  Voltmeter  for  high  tensions 109 

598  I — VIII    .     Dead-beat  Hot-wire  Ammeters  in  circular  case 99 

599  I-VII     .             „                 „         Voltmeters  „        „            „       99 

600     ....            „                 „         Volt-  and  Ammeter  combined  in  portable  case  98 

600  a  I  &  II  .            „                  „         Ammeters  as  portable  control  instruments  .     .  98 

600  b  I  &  II  .            „                  „          Voltmeters  „         „               „                  „             .     .  98 

601  ....     Standard  dead-beat  Volt-  and  Ammeter  combined  in  portable  case  94 
601  a  I  &  II  .            „             „        „      Ammeters  as  portable  control  instruments    .     .  94 

601  b  I— III    .            „             „        „      Voltmeters  „           „               „                „               .     .  94 

602  &602a  I -VIII.    Standard  dead-beat  Ammeters  in  circular  case 95 

603  &  603  a  I— VII.            ,,                  „          Voltmeters,,           „          „ 95 

604,  604  a  &  604 b.             „                  „           instrument  in  upright  cases      .....  96 

605  ....     Small  dead-beat  Accumulator  cell  tester 97 

605  a     .     .     .     Small  Standard  Milliamperemeter  for  medical  use 97 

606  ....     Differential  Voltmeter  for  direct  current 114 

606  a      .     .     .     Caloric  differential  Voltmeter  for  direct  and  alternating  current  .     .  114 

608  III— VIII.     Back  charge  and  current  Index  for  working  dynamos  in  parallel    .  116 

610  &  610a  I— IX.     Wattmeter   for  direct  and   alternating  current   in  circular  case  118 

612  I-IX.    .    Leakage  Indicator  „        „         „              „                „          „        „          „  117 

614  ....     Ohmmeter  to  read  direct  in  Ohms 52 

621  &  621  a   .     Portable  Ammeters,  Voltmeters  &c.  for  outdoor  use 132 

624  ....     Speed  counter  with  meter  measuring  wheel 134 

625  .     .     .     .         „             „             „           „               „                n       and  Chronograph     .     .  134 

627  ....     Cable  calculating  apparatus 137 

628  &  628  a   .     Apparatus  to  determine  the  sectional  area  of  mains   or  the  fall  of 

potential  therein,  Helberger  System 135 

630  III,  IV  &  VI.    Small  Electromotors  of  l!w,  '/is,  V»  HP 142 

632  HI,  IV  &  VI.     Electrically  driven  ventilating  Fans       143 

638  ....     Portable  Dynamos  for  blasting  purposes 141 

641   ....     Portable  apparatus  to  measure  resistances  and  potentials    ....  49 

660  &  660  a   .     Telephone  Stations  with  microphon  and  battery  call 140 

662  &  662  a   .             „                 „           „               „             „     magneto  call 140 


156 


41 


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LOS  Angeles  instruments  pS 

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